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Visit website Recent posts Updated on $DATE date leetcode Zola2024-12-29T00:00:00+00:00https://shaozk.xyz/tags/leetcode/atom.xml 2024-12-29T00:00:00+00:00 2024-12-29T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/14-two-sum-ii-input-array-is-sorted/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给你一个下标从 <code>1</code> 开始的整数数组 <code>numbers</code> ，该数组已按非递减顺序排列，请你从数组中找到满足相加之和等于目标数 <code>target</code> 的两个数。如果社这两个数分别是 <code>numbers[index1]</code> 和 <code>numbers[index2]</code> ，则 <code>1&lt;=index1&lt;index2&lt;=numbers.length</code> 。</p> <p>以长度为 <code>2</code> 的整数数组 <code>[index1,index2]</code> 的形式返回这两个整数的下标 <code>index1</code> 和 <code>index2</code> 。</p> <p>可以假设每个输入只对应唯一的答案，而且你不可以重复使用相同的元素。</p> <p>你所设计的解决方案只使用常量级的额外空间。</p> <p>原题链接： <a rel="external" href="https://leetcode.cn/problems/two-sum-ii-input-array-is-sorted/">167. 两数之和 II - 输入有序数组</a></p> <hr /> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-bao-li-fa">1 暴力法</h3> <h4 id="fen-xi">分析</h4> <p>因为需要查询两个值，马上可以想到使用两层遍历来分别查询结果。对于第一层循环，需要整个遍历数组，因为任何一个元素都有可能是结果之一；假定其中一个值下标为 <code>index1</code> ，则可以在剩下的数组中查找值为 <code>target-numbers[index1]</code> 的元素，其下标值即为需要查找的 <code>index2</code> 。</p> <p>由题意已知数组已排序，可使用二分查找法提高查询速度。</p> <h4 id="dai-ma">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> find</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> vec</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> left</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> right</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> n</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 二分查找</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> ret </span><span class="z-keyword z-operator">= -</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> mid </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">left </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> right</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> mid </span><span class="z-keyword z-operator">=</span><span class="z-punctuation"> (</span><span class="z-source">left </span><span class="z-keyword z-operator">+</span><span class="z-source"> right</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> /</span><span class="z-constant z-numeric"> 2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">vec</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">mid</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> ==</span><span class="z-source"> n</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> ret </span><span class="z-keyword z-operator">=</span><span class="z-source"> mid</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> break</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else if</span><span class="z-punctuation"> (</span><span class="z-source">vec</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">mid</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> &gt;</span><span class="z-source"> n</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> right </span><span class="z-keyword z-operator">=</span><span class="z-source"> mid</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> left </span><span class="z-keyword z-operator">=</span><span class="z-source"> mid </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> ret</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type"> vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-entity z-name z-function"> twoSum</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> numbers</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> target</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> idx1 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> idx2 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> num </span><span class="z-keyword z-operator">=</span><span class="z-source"> numbers</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-source">idx1 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> idx1 </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> num</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">idx1</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历数组</span></span> <span class="giallo-l"><span class="z-source"> idx2 </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> find</span><span class="z-punctuation">(</span><span class="z-source">numbers</span><span class="z-punctuation">,</span><span class="z-source"> idx1 </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">,</span><span class="z-source"> num</span><span class="z-punctuation">,</span><span class="z-source"> target </span><span class="z-keyword z-operator">-</span><span class="z-source"> numbers</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">idx1</span><span class="z-punctuation">));</span><span class="z-punctuation z-definition z-comment z-comment"> // 二分查找</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">idx2 </span><span class="z-keyword z-operator">!= -</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">) {</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> break</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 找到直接终止循环</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-punctuation"> {</span><span class="z-source">idx1 </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">,</span><span class="z-source"> idx2 </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">};</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(logn)</code> ，遍历第一个元素需要 <code>O(n)</code> 时间，查找第二个元素需要 <code>O(logn)</code> 时间；二者结合 <code>O(nlogn)</code></p> </li> <li> <p>空间复杂度： <code>O(1)</code> ，只使用常量空间。</p> </li> </ul> <h3 id="2-shuang-zhi-zhen">2 双指针</h3> <h4 id="fen-xi-1">分析</h4> <p>已知结果唯一且数组有序，因此可以设定两个指针分别指向数组的首尾，指针从两头往中间靠拢，直到找到满足条件的结果。当两指针指向元素和为结果值，返回结果；当元素和小于结果值，更新左指针（++）；当元素和大于结果值，更新右指针（–）。</p> <h4 id="dai-ma-1">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-entity z-name z-function"> twoSum</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> numbers</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> target</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> idx1 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> idx2 </span><span class="z-keyword z-operator">=</span><span class="z-source"> numbers</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> -</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 定义指向首尾的指针</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">idx1 </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> idx2</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历数组</span></span> <span class="giallo-l"><span class="z-storage z-type"> auto</span><span class="z-source"> sum </span><span class="z-keyword z-operator">=</span><span class="z-source"> numbers</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">idx1</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> +</span><span class="z-source"> numbers</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">idx2</span><span class="z-punctuation">);</span><span class="z-punctuation z-definition z-comment z-comment"> // 计算两数和</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">sum </span><span class="z-keyword z-operator">==</span><span class="z-source"> target</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 判断是否是目标值</span></span> <span class="giallo-l"><span class="z-keyword"> break</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else if</span><span class="z-punctuation"> (</span><span class="z-source">sum </span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> target</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 判断是否比目标值大</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> --</span><span class="z-source">idx2</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新idx2</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else</span><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-comment z-comment"> // 判断是否比目标值小</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">idx1</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新idx1</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-punctuation"> {</span><span class="z-source">idx1 </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">,</span><span class="z-source"> idx2 </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">};</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回结果数组（需要替换为从1开始的下标）</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du-1">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(n)</code> ，双指针移动的总次数不超过 <code>n</code></p> </li> <li> <p>空间复杂度： <code>O(1)</code> ，常量空间使用。</p> </li> </ul> <hr /> <h2 id="san-zong-jie">三 总结</h2> <ul> <li> <p>当需要在有序数组上进行查询操作时，二分查找是个不错的选择。</p> </li> <li> <p>双指针法也适合在有序数组上使用。</p> </li> </ul> <hr /> 2024-12-18T00:00:00+00:00 2024-12-18T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/13-gopl-chapter-1-tutorial/ <h2 id="1-ru-men">1.入门</h2> <h3 id="lian-xi-ti">练习题</h3> <h4 id="1-1">1.1</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习1.1: 修改 echo 程序，使其能够打印 os.Args[0]，即被执行命令本身的名字。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">package main</span><span class="z-punctuation z-definition z-comment z-comment"> // 声明包</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入包fmt（格式化输出）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入包os（获取命令行参数）</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span><span class="z-punctuation z-definition z-comment z-comment"> // 主函数</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Println</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 打印所有参数（包括程序本身）</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 输出</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 注：符号‘#’除注释外，还代表输入的命令</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 进入到.go源文件所在目录，输入go build即可运行（无需指定源文件）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># -o 用于指定生成的可执行文件（默认以文件夹名作为文件名）</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_1#</span><span class="z-string"> go build -o a.out</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_1#</span><span class="z-string"> ./a.out arg1 arg2 arg3</span></span> <span class="giallo-l"><span class="z-punctuation">[</span><span class="z-source">./a.out arg1 arg2 arg3</span><span class="z-punctuation">]</span></span> <span class="giallo-l"></span></code></pre><h4 id="1-2">1.2</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.2: 修改 echo 程序，使其打印每个参数的索引和值，每个一行。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> idx</span><span class="z-punctuation">,</span><span class="z-source"> value</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历命令行参数</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Println</span><span class="z-punctuation">(</span><span class="z-source">idx</span><span class="z-punctuation">,</span><span class="z-source"> value</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 打印索引和参数</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 编译命令同上，故省略</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_2#</span><span class="z-string"> ./a.out arg1 arg2 arg3</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0</span><span class="z-string"> ./a.out</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">1</span><span class="z-string"> arg1</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">2</span><span class="z-string"> arg2</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">3</span><span class="z-string"> arg3</span></span></code></pre><h4 id="1-3">1.3</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.3: 做实验测量潜在低效的版本和使用了 strings.Join 的版本的运行时间差异。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;time&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入包time（计时器）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;strings&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入包strings（字符串）</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-source"> start1</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> time</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Now</span><span class="z-punctuation">()</span><span class="z-punctuation z-definition z-comment z-comment"> // 计时器1，用于计算老方法时间开销</span></span> <span class="giallo-l"><span class="z-source"> str</span><span class="z-punctuation">,</span><span class="z-source"> sep</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-punctuation z-definition z-string"> &quot;&quot;</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string"> &quot;&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化str存储连接后的字符串，初始化sep存储空格</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> arg</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> str </span><span class="z-keyword z-operator">+=</span><span class="z-source"> sep </span><span class="z-keyword z-operator">+</span><span class="z-source"> arg</span><span class="z-punctuation z-definition z-comment z-comment"> // 连接参数字符串</span></span> <span class="giallo-l"><span class="z-source"> sep </span><span class="z-keyword z-operator">=</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 经过一个参数后，sep换为空格</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Println</span><span class="z-punctuation">(</span><span class="z-source">str</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 输出连接后的值</span></span> <span class="giallo-l"><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Printf</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;old way: %dns elapsed</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> time</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Since</span><span class="z-punctuation">(</span><span class="z-source">start1</span><span class="z-punctuation">).</span><span class="z-entity z-name z-function">Nanoseconds</span><span class="z-punctuation">())</span><span class="z-punctuation z-definition z-comment z-comment"> // 打印时间开销</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source"> start2</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> time</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Now</span><span class="z-punctuation">()</span><span class="z-punctuation z-definition z-comment z-comment"> // 计时器2，用于计算新方法时间开销</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Println</span><span class="z-punctuation">(</span><span class="z-source">strings</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Join</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-punctuation">))</span><span class="z-punctuation z-definition z-comment z-comment"> // 输出连接后的值</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Printf</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;new way: %dns elapsed</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> time</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Since</span><span class="z-punctuation">(</span><span class="z-source">start2</span><span class="z-punctuation">).</span><span class="z-entity z-name z-function">Nanoseconds</span><span class="z-punctuation">())</span><span class="z-punctuation z-definition z-comment z-comment"> // 打印时间开销</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_3#</span><span class="z-string"> go build -o a.out</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_3#</span><span class="z-string"> ./a.out arg1 arg2 arg3</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">./a.out</span><span class="z-string"> arg1 arg2 arg3</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">old</span><span class="z-string"> way: 113583ns elapsed</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">./a.out</span><span class="z-string"> arg1 arg2 arg3</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">new</span><span class="z-string"> way: 2584ns elapsed</span></span></code></pre><h4 id="1-4">1.4</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.4: 修改 dup2，出现重复的行时打印文件名称</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// Dup2 prints the count and text of lines that appear more than once</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// in the input. It reads from stdin or from a list of named files.</span></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;bufio&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入bufio包（标准输入）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 自定义计数器</span></span> <span class="giallo-l"><span class="z-source">type MyCount </span><span class="z-storage z-type">struct</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> count</span><span class="z-storage z-type"> int</span><span class="z-punctuation z-definition z-comment z-comment"> // 记录行数</span></span> <span class="giallo-l"><span class="z-source"> names []string</span><span class="z-punctuation z-definition z-comment z-comment"> // 记录行所在文件</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-source"> counts</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> make</span><span class="z-punctuation">(</span><span class="z-source">map</span><span class="z-punctuation">[</span><span class="z-source">string</span><span class="z-punctuation">]</span><span class="z-keyword z-operator">*</span><span class="z-source">MyCount</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 构造&lt;string,MyCount*&gt;字典</span></span> <span class="giallo-l"><span class="z-source"> files</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">1</span><span class="z-source">:</span><span class="z-punctuation">]</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-entity z-name z-function"> len</span><span class="z-punctuation">(</span><span class="z-source">files</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> ==</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-comment z-comment"> // 判断是否包含文件</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> countLines</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stdin</span><span class="z-punctuation">,</span><span class="z-source"> counts</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 从标准输入获取行</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> arg</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range files </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> f</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> os</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Open</span><span class="z-punctuation">(</span><span class="z-source">arg</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 打开文件</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> err </span><span class="z-keyword z-operator">!=</span><span class="z-source"> nil </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stderr</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;dup2: %v</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-keyword"> continue</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> countLines</span><span class="z-punctuation">(</span><span class="z-source">f</span><span class="z-punctuation">,</span><span class="z-source"> counts</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 从文件获取行</span></span> <span class="giallo-l"><span class="z-source"> f</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Close</span><span class="z-punctuation">()</span><span class="z-punctuation z-definition z-comment z-comment"> // 关闭文件</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> printLines</span><span class="z-punctuation">(</span><span class="z-source">counts</span><span class="z-punctuation">,</span><span class="z-entity z-name z-function"> len</span><span class="z-punctuation">(</span><span class="z-source">files</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> !=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 输出字典</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 构建以字符串为值、以自定义计数器为键的map</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 按行获取字符串，判断map中是否包含该字符串，是则计数+1，将文件名添加到列表中（如果不存在）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 否则新键一个键值对插入到map中</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// [in] f 文件</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// [out] counts 自定义计数器map </span></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> countLines</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">f</span><span class="z-storage z-modifier"> *</span><span class="z-entity z-name z-type">os</span><span class="z-source">.</span><span class="z-variable z-parameter">File</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> counts</span><span class="z-variable z-parameter"> map</span><span class="z-punctuation">[</span><span class="z-source">string</span><span class="z-punctuation">]</span><span class="z-storage z-modifier">*</span><span class="z-variable z-parameter">MyCount</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> input</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> bufio</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">NewScanner</span><span class="z-punctuation">(</span><span class="z-source">f</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> input</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Scan</span><span class="z-punctuation">() {</span><span class="z-punctuation z-definition z-comment z-comment"> // 按行扫描</span></span> <span class="giallo-l"><span class="z-source"> line</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> input</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Text</span><span class="z-punctuation">()</span><span class="z-punctuation z-definition z-comment z-comment"> // 获取文本</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> ok</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> counts</span><span class="z-punctuation">[</span><span class="z-source">line</span><span class="z-punctuation">];</span><span class="z-source"> ok </span><span class="z-punctuation">{</span><span class="z-punctuation z-definition z-comment z-comment"> // 如果字典中存在该字符串</span></span> <span class="giallo-l"><span class="z-source"> counts</span><span class="z-punctuation">[</span><span class="z-source">line</span><span class="z-punctuation">].</span><span class="z-source">count</span><span class="z-keyword z-operator">++</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 计数加1</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-keyword z-operator"> !</span><span class="z-entity z-name z-function">contains</span><span class="z-punctuation">(</span><span class="z-source">counts</span><span class="z-punctuation">[</span><span class="z-source">line</span><span class="z-punctuation">].</span><span class="z-source">names</span><span class="z-punctuation">,</span><span class="z-source"> f</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Name</span><span class="z-punctuation">()) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 判断是否已经包含文件名</span></span> <span class="giallo-l"><span class="z-source"> counts</span><span class="z-punctuation">[</span><span class="z-source">line</span><span class="z-punctuation">].</span><span class="z-source">names</span><span class="z-keyword z-operator"> =</span><span class="z-entity z-name z-function"> append</span><span class="z-punctuation">(</span><span class="z-source">counts</span><span class="z-punctuation">[</span><span class="z-source">line</span><span class="z-punctuation">].</span><span class="z-source">names</span><span class="z-punctuation">,</span><span class="z-source"> f</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Name</span><span class="z-punctuation">())</span><span class="z-punctuation z-definition z-comment z-comment"> // 添加文件名</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> counts</span><span class="z-punctuation">[</span><span class="z-source">line</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> = &amp;</span><span class="z-source">MyCount</span><span class="z-punctuation">{</span><span class="z-punctuation z-definition z-comment z-comment"> // 插入新键-值对</span></span> <span class="giallo-l"><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-comment z-comment"> // 计数为1</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> make</span><span class="z-punctuation">([]</span><span class="z-source">string, 1), // 空的字符串数组</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-source"> counts</span><span class="z-punctuation">[</span><span class="z-source">line</span><span class="z-punctuation">].</span><span class="z-source">names</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> =</span><span class="z-source"> f</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Name</span><span class="z-punctuation">()</span><span class="z-punctuation z-definition z-comment z-comment"> // 填充字符串数组</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // NOTE: ignoring potential errors from input.Err()</span></span> <span class="giallo-l"><span class="z-source">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 根据是否是文件输出自定义计数器map</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// [in] counts 自定义计数器map</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// [in] flagFile 文件标志</span></span> <span class="giallo-l"><span class="z-source">func</span><span class="z-entity z-name z-function"> printLines</span><span class="z-punctuation">(</span><span class="z-source">counts map</span><span class="z-punctuation">[</span><span class="z-source">string</span><span class="z-punctuation">]</span><span class="z-keyword z-operator">*</span><span class="z-source">MyCount</span><span class="z-punctuation">,</span><span class="z-source"> flagFile</span><span class="z-storage z-type"> bool</span><span class="z-punctuation">)</span><span class="z-source"> {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> line</span><span class="z-punctuation">,</span><span class="z-source"> c :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range counts {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> c</span><span class="z-punctuation">.</span><span class="z-source">count</span><span class="z-keyword z-operator"> &gt;</span><span class="z-constant z-numeric"> 1</span><span class="z-source"> {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> flagFile {</span><span class="z-punctuation z-definition z-comment z-comment"> // 判断是否由文件读取</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Printf</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;%d</span><span class="z-constant z-character z-escape">\t</span><span class="z-string">%s</span><span class="z-constant z-character z-escape">\t</span><span class="z-string">%v</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> c</span><span class="z-punctuation">.</span><span class="z-source">count</span><span class="z-punctuation">,</span><span class="z-source"> line</span><span class="z-punctuation">,</span><span class="z-source"> c</span><span class="z-punctuation">.</span><span class="z-source">names</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> }</span><span class="z-keyword"> else</span><span class="z-source"> {</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Printf</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;%d</span><span class="z-constant z-character z-escape">\t</span><span class="z-string">%s</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> c</span><span class="z-punctuation">.</span><span class="z-source">count</span><span class="z-punctuation">,</span><span class="z-source"> line</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-source">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 判断字符串数组是否包含某一个字符串(暴力法)</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// [in] slice 字符串数组</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// [in] s 字符串</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// [out] 返回是否包含</span></span> <span class="giallo-l"><span class="z-source">func</span><span class="z-entity z-name z-function"> contains</span><span class="z-punctuation">(</span><span class="z-source">slice []string</span><span class="z-punctuation">,</span><span class="z-source"> s string</span><span class="z-punctuation">)</span><span class="z-storage z-type"> bool</span><span class="z-source"> {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> value :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range slice {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> value </span><span class="z-keyword z-operator">==</span><span class="z-source"> s {</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-true"> true</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source">}</span></span> <span class="giallo-l"></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_4#</span><span class="z-string"> cat test1.txt</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">b</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">b</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">c</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_4#</span><span class="z-string"> cat test2.txt</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">a</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">a</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">b</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">b</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">b</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">c</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_4#</span><span class="z-string"> ./a.out test1.txt test2.txt</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">2</span><span class="z-string"> c</span><span class="z-source"> [test1.txt</span><span class="z-string"> test2.txt]</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">2</span><span class="z-string"> a</span><span class="z-source"> [test2.txt]</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">5</span><span class="z-string"> b</span><span class="z-source"> [test1.txt</span><span class="z-string"> test2.txt]</span></span></code></pre><h4 id="1-5">1.5</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.5: 修改前面的Lissajous程序里的调色板，由黑色改为绿色。</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 我们可以用color.RGBA{0xRR, 0xGG, 0xBB, 0xff}来得到#RRGGBB这个色值，</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 三个十六进制的字符串分别代表红、绿、蓝像素。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// Lissajous generates GIF animations of random Lissajous figures.</span></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入image包（图像处理）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image/color&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入image下的子包color（颜色）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image/gif&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入gif包（动图）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;io&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;math&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入math包（数学）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;math/rand&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 导入rand包（随机数）</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;time&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">var palette </span><span class="z-keyword z-operator">=</span><span class="z-punctuation"> []</span><span class="z-source">color.Color</span><span class="z-punctuation">{</span><span class="z-source">color</span><span class="z-punctuation">.</span><span class="z-source">White</span><span class="z-punctuation">,</span><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">Black</span><span class="z-punctuation">,</span><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">RGBA</span><span class="z-punctuation">{</span><span class="z-keyword">0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">}}</span><span class="z-punctuation z-definition z-comment z-comment"> // 颜色数组</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier">const</span><span class="z-punctuation"> (</span></span> <span class="giallo-l"><span class="z-source"> whiteIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-definition z-comment z-comment"> // first color in palette</span></span> <span class="giallo-l"><span class="z-source"> blackIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation z-definition z-comment z-comment"> // next color in palette</span></span> <span class="giallo-l"><span class="z-source"> greenIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 2</span><span class="z-punctuation z-definition z-comment z-comment"> // 绿色</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // The sequence of images is deterministic unless we seed</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // the pseudo-random number generator using the current time.</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // Thanks to Randall McPherson for pointing out the omission.</span></span> <span class="giallo-l"><span class="z-source"> rand</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Seed</span><span class="z-punctuation">(</span><span class="z-source">time</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Now</span><span class="z-punctuation">().</span><span class="z-entity z-name z-function">UTC</span><span class="z-punctuation">().</span><span class="z-entity z-name z-function">UnixNano</span><span class="z-punctuation">())</span><span class="z-punctuation z-definition z-comment z-comment"> // 使用当前时间生成随机数</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> lissajous</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stdout</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> lissajous</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">out io</span><span class="z-source">.</span><span class="z-variable z-parameter">Writer</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-punctuation"> (</span></span> <span class="giallo-l"><span class="z-source"> cycles </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 5</span><span class="z-punctuation z-definition z-comment z-comment"> // number of complete x oscillator revolutions</span></span> <span class="giallo-l"><span class="z-source"> res </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.001</span><span class="z-punctuation z-definition z-comment z-comment"> // angular resolution</span></span> <span class="giallo-l"><span class="z-source"> size </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 100</span><span class="z-punctuation z-definition z-comment z-comment"> // image canvas covers [-size..+size]</span></span> <span class="giallo-l"><span class="z-source"> nframes </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 64</span><span class="z-punctuation z-definition z-comment z-comment"> // number of animation frames</span></span> <span class="giallo-l"><span class="z-source"> delay </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 8</span><span class="z-punctuation z-definition z-comment z-comment"> // delay between frames in 10ms units</span></span> <span class="giallo-l"><span class="z-punctuation"> )</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source"> freq</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> rand</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Float64</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> *</span><span class="z-constant z-numeric"> 3.0</span><span class="z-punctuation z-definition z-comment z-comment"> // relative frequency of y oscillator</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> gif</span><span class="z-punctuation">.</span><span class="z-source">GIF</span><span class="z-punctuation">{</span><span class="z-source">LoopCount</span><span class="z-punctuation">:</span><span class="z-source"> nframes</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-source"> phase</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.0</span><span class="z-punctuation z-definition z-comment z-comment"> // phase difference</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> i</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> nframes</span><span class="z-punctuation">;</span><span class="z-source"> i</span><span class="z-keyword z-operator">++</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> rect</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> image</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Rect</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 2</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 2</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> img</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> image</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">NewPaletted</span><span class="z-punctuation">(</span><span class="z-source">rect</span><span class="z-punctuation">,</span><span class="z-source"> palette</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> t</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.0</span><span class="z-punctuation">;</span><span class="z-source"> t </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> cycles</span><span class="z-keyword z-operator">*</span><span class="z-constant z-numeric">2</span><span class="z-keyword z-operator">*</span><span class="z-source">math</span><span class="z-punctuation">.</span><span class="z-source">Pi</span><span class="z-punctuation">;</span><span class="z-source"> t </span><span class="z-keyword z-operator">+=</span><span class="z-source"> res </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> x</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> math</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Sin</span><span class="z-punctuation">(</span><span class="z-source">t</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> y</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> math</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Sin</span><span class="z-punctuation">(</span><span class="z-source">t</span><span class="z-keyword z-operator">*</span><span class="z-source">freq </span><span class="z-keyword z-operator">+</span><span class="z-source"> phase</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> img</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">SetColorIndex</span><span class="z-punctuation">(</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-storage z-type">int</span><span class="z-punctuation">(</span><span class="z-source">x</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">0.5</span><span class="z-punctuation">),</span><span class="z-source"> size</span><span class="z-keyword z-operator">+</span><span class="z-storage z-type">int</span><span class="z-punctuation">(</span><span class="z-source">y</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">0.5</span><span class="z-punctuation">),</span></span> <span class="giallo-l"><span class="z-source"> greenIndex</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> phase </span><span class="z-keyword z-operator">+=</span><span class="z-constant z-numeric"> 0.1</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation">.</span><span class="z-source">Delay</span><span class="z-keyword z-operator"> =</span><span class="z-entity z-name z-function"> append</span><span class="z-punctuation">(</span><span class="z-source">anim</span><span class="z-punctuation">.</span><span class="z-source">Delay</span><span class="z-punctuation">,</span><span class="z-source"> delay</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation">.</span><span class="z-source">Image</span><span class="z-keyword z-operator"> =</span><span class="z-entity z-name z-function"> append</span><span class="z-punctuation">(</span><span class="z-source">anim</span><span class="z-punctuation">.</span><span class="z-source">Image</span><span class="z-punctuation">,</span><span class="z-source"> img</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> gif</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">EncodeAll</span><span class="z-punctuation">(</span><span class="z-source">out</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> &amp;</span><span class="z-source">anim</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // NOTE: ignoring encoding errors</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_5#</span><span class="z-string"> ./a.out</span><span class="z-keyword z-operator"> &gt;</span><span class="z-string">out.gif</span></span></code></pre> <p><img src="/csdn/13_1.gif" alt="在这里插入图片描述" /></p> <h4 id="1-6">1.6</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.6: 修改Lissajous程序，修改其调色板来生成更丰富的颜色，</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 然后修改SetColorIndex的第三个参数，看看显示结果吧。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// Lissajous generates GIF animations of random Lissajous figures.</span></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image/color&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image/gif&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;io&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;math&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;math/rand&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;time&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">var palette </span><span class="z-keyword z-operator">=</span><span class="z-punctuation"> []</span><span class="z-source">color.Color</span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">White</span><span class="z-punctuation">,</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">Black</span><span class="z-punctuation">,</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">RGBA</span><span class="z-punctuation">{</span><span class="z-keyword">0x</span><span class="z-constant z-numeric">11</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">22</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">33</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">},</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">RGBA</span><span class="z-punctuation">{</span><span class="z-keyword">0x</span><span class="z-constant z-numeric">aa</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">bb</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">cc</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">RGBA</span><span class="z-punctuation">{</span><span class="z-keyword">0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">bb</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">RGBA</span><span class="z-punctuation">{</span><span class="z-keyword">0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">},</span><span class="z-punctuation z-definition z-comment z-comment"> // 红</span></span> <span class="giallo-l"><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">RGBA</span><span class="z-punctuation">{</span><span class="z-keyword">0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">},</span><span class="z-punctuation z-definition z-comment z-comment"> // 绿</span></span> <span class="giallo-l"><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">RGBA</span><span class="z-punctuation">{</span><span class="z-keyword">0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">},</span><span class="z-punctuation z-definition z-comment z-comment"> // 蓝</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier">const</span><span class="z-punctuation"> (</span></span> <span class="giallo-l"><span class="z-source"> whiteIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-definition z-comment z-comment"> // first color in palette</span></span> <span class="giallo-l"><span class="z-source"> blackIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation z-definition z-comment z-comment"> // next color in palette</span></span> <span class="giallo-l"><span class="z-source"> color1 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 2</span></span> <span class="giallo-l"><span class="z-source"> color2 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 3</span></span> <span class="giallo-l"><span class="z-source"> color3 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 4</span></span> <span class="giallo-l"><span class="z-source"> redIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 5</span></span> <span class="giallo-l"><span class="z-source"> greenIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 6</span></span> <span class="giallo-l"><span class="z-source"> blueIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 7</span></span> <span class="giallo-l"><span class="z-source"> colorNum </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 8</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // The sequence of images is deterministic unless we seed</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // the pseudo-random number generator using the current time.</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // Thanks to Randall McPherson for pointing out the omission.</span></span> <span class="giallo-l"><span class="z-source"> rand</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Seed</span><span class="z-punctuation">(</span><span class="z-source">time</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Now</span><span class="z-punctuation">().</span><span class="z-entity z-name z-function">UTC</span><span class="z-punctuation">().</span><span class="z-entity z-name z-function">UnixNano</span><span class="z-punctuation">())</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> lissajous</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stdout</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> lissajous</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">out io</span><span class="z-source">.</span><span class="z-variable z-parameter">Writer</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-punctuation"> (</span></span> <span class="giallo-l"><span class="z-source"> cycles </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 5</span><span class="z-punctuation z-definition z-comment z-comment"> // number of complete x oscillator revolutions</span></span> <span class="giallo-l"><span class="z-source"> res </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.001</span><span class="z-punctuation z-definition z-comment z-comment"> // angular resolution</span></span> <span class="giallo-l"><span class="z-source"> size </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 100</span><span class="z-punctuation z-definition z-comment z-comment"> // image canvas covers [-size..+size]</span></span> <span class="giallo-l"><span class="z-source"> nframes </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 64</span><span class="z-punctuation z-definition z-comment z-comment"> // number of animation frames</span></span> <span class="giallo-l"><span class="z-source"> delay </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 8</span><span class="z-punctuation z-definition z-comment z-comment"> // delay between frames in 10ms units</span></span> <span class="giallo-l"><span class="z-punctuation"> )</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source"> freq</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> rand</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Float64</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> *</span><span class="z-constant z-numeric"> 3.0</span><span class="z-punctuation z-definition z-comment z-comment"> // relative frequency of y oscillator</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> gif</span><span class="z-punctuation">.</span><span class="z-source">GIF</span><span class="z-punctuation">{</span><span class="z-source">LoopCount</span><span class="z-punctuation">:</span><span class="z-source"> nframes</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-source"> phase</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.0</span><span class="z-punctuation z-definition z-comment z-comment"> // phase difference</span></span> <span class="giallo-l"><span class="z-source"> colorIndex</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> uint8</span><span class="z-punctuation">(</span><span class="z-source">whiteIndex</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> i</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> nframes</span><span class="z-punctuation">;</span><span class="z-source"> i</span><span class="z-keyword z-operator">++</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> rect</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> image</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Rect</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 2</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 2</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> img</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> image</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">NewPaletted</span><span class="z-punctuation">(</span><span class="z-source">rect</span><span class="z-punctuation">,</span><span class="z-source"> palette</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> t</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.0</span><span class="z-punctuation">;</span><span class="z-source"> t </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> cycles</span><span class="z-keyword z-operator">*</span><span class="z-constant z-numeric">2</span><span class="z-keyword z-operator">*</span><span class="z-source">math</span><span class="z-punctuation">.</span><span class="z-source">Pi</span><span class="z-punctuation">;</span><span class="z-source"> t </span><span class="z-keyword z-operator">+=</span><span class="z-source"> res </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> x</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> math</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Sin</span><span class="z-punctuation">(</span><span class="z-source">t</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> y</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> math</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Sin</span><span class="z-punctuation">(</span><span class="z-source">t</span><span class="z-keyword z-operator">*</span><span class="z-source">freq </span><span class="z-keyword z-operator">+</span><span class="z-source"> phase</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> img</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">SetColorIndex</span><span class="z-punctuation">(</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-storage z-type">int</span><span class="z-punctuation">(</span><span class="z-source">x</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">0.5</span><span class="z-punctuation">),</span><span class="z-source"> size</span><span class="z-keyword z-operator">+</span><span class="z-storage z-type">int</span><span class="z-punctuation">(</span><span class="z-source">y</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">0.5</span><span class="z-punctuation">),</span></span> <span class="giallo-l"><span class="z-source"> colorIndex</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> colorIndex </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> uint8</span><span class="z-punctuation">(</span><span class="z-source">i </span><span class="z-keyword z-operator">%</span><span class="z-source"> colorNum</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 动态更新颜色</span></span> <span class="giallo-l"><span class="z-source"> phase </span><span class="z-keyword z-operator">+=</span><span class="z-constant z-numeric"> 0.1</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation">.</span><span class="z-source">Delay</span><span class="z-keyword z-operator"> =</span><span class="z-entity z-name z-function"> append</span><span class="z-punctuation">(</span><span class="z-source">anim</span><span class="z-punctuation">.</span><span class="z-source">Delay</span><span class="z-punctuation">,</span><span class="z-source"> delay</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation">.</span><span class="z-source">Image</span><span class="z-keyword z-operator"> =</span><span class="z-entity z-name z-function"> append</span><span class="z-punctuation">(</span><span class="z-source">anim</span><span class="z-punctuation">.</span><span class="z-source">Image</span><span class="z-punctuation">,</span><span class="z-source"> img</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> gif</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">EncodeAll</span><span class="z-punctuation">(</span><span class="z-source">out</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> &amp;</span><span class="z-source">anim</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // NOTE: ignoring encoding errors</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_6#</span><span class="z-string"> ./a.out</span><span class="z-keyword z-operator"> &gt;</span><span class="z-string"> out.gif</span></span></code></pre> <p><img src="/csdn/13_2.gif" alt="在这里插入图片描述" /></p> <h4 id="1-7">1.7</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.7： 函数调用io.Copy(dst, src)会从src中读取内容，并将读到的结果</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 写入到dst中，使用这个函数替代掉例子中的ioutil.ReadAll来拷贝响应结构体到</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// os.Stdout，避免申请一个缓冲区（例子中的b）来存储。记得处理io.Copy返回结</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 果中的错误。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// Fetch prints the content found at a URL.</span></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;io&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;net/http&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 网络</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> url</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">1</span><span class="z-source">:</span><span class="z-punctuation">] {</span></span> <span class="giallo-l"><span class="z-source"> resp</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> http</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Get</span><span class="z-punctuation">(</span><span class="z-source">url</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> err </span><span class="z-keyword z-operator">!=</span><span class="z-source"> nil </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stderr</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;fetch: %v</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> os</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Exit</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // b, err := io.ReadAll(resp.Body)</span></span> <span class="giallo-l"><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> err </span><span class="z-keyword z-operator">=</span><span class="z-source"> io</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Copy</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stdout</span><span class="z-punctuation">,</span><span class="z-source"> resp</span><span class="z-punctuation">.</span><span class="z-source">Body</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 拷贝数据到标准输出</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> err </span><span class="z-keyword z-operator">!=</span><span class="z-source"> nil </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stderr</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;fetch: reading %s: %v</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> url</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> os</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Exit</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> resp</span><span class="z-punctuation">.</span><span class="z-source">Body</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Close</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_7#</span><span class="z-string"> ./a.out https://www.baidu.com</span></span> <span class="giallo-l"><span class="z-keyword z-operator">&lt;!</span><span class="z-entity z-name z-function">DOCTYPE</span><span class="z-string"> htm</span><span class="z-source">l</span><span class="z-keyword z-operator">&gt;</span></span> <span class="giallo-l"><span class="z-keyword z-operator">&lt;!</span><span class="z-entity z-name z-function">--STATUS</span><span class="z-string"> OK-</span><span class="z-source">-&gt;&lt;</span><span class="z-string">htm</span><span class="z-source">l</span><span class="z-keyword z-operator">&gt; &lt;</span><span class="z-string">hea</span><span class="z-source">d&gt;&lt;</span><span class="z-string">meta http-equiv=content-type content=text/html</span><span class="z-punctuation">;</span><span class="z-source">charset</span><span class="z-keyword z-operator">=</span><span class="z-string">utf-8</span><span class="z-source">&gt;&lt;</span><span class="z-string">meta</span><span class="z-source"> http-equiv</span><span class="z-keyword z-operator">=</span><span class="z-string">X-UA-Compatible</span><span class="z-source"> content</span><span class="z-keyword z-operator">=</span><span class="z-source">IE</span><span class="z-keyword z-operator">=</span><span class="z-string">Edge</span><span class="z-source">&gt;&lt;</span><span class="z-string">meta</span><span class="z-source"> content</span><span class="z-keyword z-operator">=</span><span class="z-string">always</span><span class="z-source"> name</span><span class="z-keyword z-operator">=</span><span class="z-string">referrer</span><span class="z-source">&gt;&lt;</span><span class="z-string">link</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-support z-function z-builtin">...</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_7#</span><span class="z-source"> </span></span></code></pre><h4 id="1-8">1.8</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.8: 修改fetch这个范例，如果输入的url参数没有 http:// 前缀的话，</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 为这个url加上该前缀。你可能会用到strings.HasPrefix这个函数。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// Fetch prints the content found at a URL.</span></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;io&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;strings&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;net/http&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> url</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">1</span><span class="z-source">:</span><span class="z-punctuation">] {</span></span> <span class="giallo-l"><span class="z-source"> prefix</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-punctuation z-definition z-string z-string"> &quot;https://&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 定义http前缀</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-keyword z-operator"> !</span><span class="z-source">strings</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">HasPrefix</span><span class="z-punctuation">(</span><span class="z-source">url</span><span class="z-punctuation">,</span><span class="z-source"> prefix</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 判断是否存在http前缀</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Println</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;No prefix, add &quot;</span><span class="z-punctuation">,</span><span class="z-source"> prefix</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> url </span><span class="z-keyword z-operator">=</span><span class="z-source"> prefix </span><span class="z-keyword z-operator">+</span><span class="z-source"> url</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 不是则添加上http前缀</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> resp</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> http</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Get</span><span class="z-punctuation">(</span><span class="z-source">url</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 请求访问，获取响应报文</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> err </span><span class="z-keyword z-operator">!=</span><span class="z-source"> nil </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stderr</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;fetch: %v</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> os</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Exit</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> b</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> io</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">ReadAll</span><span class="z-punctuation">(</span><span class="z-source">resp</span><span class="z-punctuation">.</span><span class="z-source">Body</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 读取响应报文</span></span> <span class="giallo-l"><span class="z-source"> resp</span><span class="z-punctuation">.</span><span class="z-source">Body</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Close</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> err </span><span class="z-keyword z-operator">!=</span><span class="z-source"> nil </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stderr</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;fetch: reading %s: %v</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> url</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> os</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Exit</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Printf</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;%s&quot;</span><span class="z-punctuation">,</span><span class="z-source"> b</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_8#</span><span class="z-string"> ./a.out www.baidu.com</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">No</span><span class="z-string"> prefix, add https://</span></span> <span class="giallo-l"><span class="z-keyword z-operator">&lt;!</span><span class="z-entity z-name z-function">DOCTYPE</span><span class="z-string"> htm</span><span class="z-source">l</span><span class="z-keyword z-operator">&gt;</span></span> <span class="giallo-l"><span class="z-keyword z-operator">&lt;!</span><span class="z-entity z-name z-function">--STATUS</span><span class="z-string"> OK-</span><span class="z-source">-&gt;&lt;</span><span class="z-string">htm</span><span class="z-source">l</span><span class="z-keyword z-operator">&gt; &lt;</span><span class="z-string">hea</span><span class="z-source">d&gt;&lt;</span><span class="z-string">meta http-equiv=content-type content=text/html</span><span class="z-punctuation">;</span><span class="z-source">charset</span><span class="z-keyword z-operator">=</span><span class="z-string">utf-8</span><span class="z-source">&gt;&lt;</span><span class="z-string">meta</span><span class="z-source"> http-equiv</span><span class="z-keyword z-operator">=</span><span class="z-string">X-UA-Compatible</span><span class="z-source"> content</span><span class="z-keyword z-operator">=</span><span class="z-source">IE</span><span class="z-keyword z-operator">=</span><span class="z-string">Edge</span><span class="z-source">&gt;&lt;</span><span class="z-string">meta</span><span class="z-source"> content</span><span class="z-keyword z-operator">=</span><span class="z-string">always</span><span class="z-source"> name</span><span class="z-keyword z-operator">=</span><span class="z-string">referrer</span><span class="z-source">&gt;&lt;</span><span class="z-string">link</span><span class="z-source"> rel</span><span class="z-keyword z-operator">=</span><span class="z-string">stylesheet</span><span class="z-source"> type</span><span class="z-keyword z-operator">=</span><span class="z-string">text/css</span><span class="z-source"> href</span><span class="z-keyword z-operator">=</span><span class="z-string">https://ss1.bdstatic.com/5eN1bjq8AAUYm2zgoY3K/r/www/cache/bdorz/baidu.min.css</span><span class="z-source">&gt;&lt;</span><span class="z-string">title</span><span class="z-keyword z-operator">&gt;</span><span class="z-string">百度一下，你就知道</span><span class="z-keyword z-operator">&lt;</span><span class="z-string">/title</span><span class="z-source">&gt;&lt;</span><span class="z-string">/head</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> &lt;body link=#0000cc&gt; &lt;div id=wrapper&gt; &lt;div id=head&gt; &lt;div class=head_wrapper&gt; &lt;div class=s_form&gt; &lt;div class=s_form_wrapper&gt; &lt;div id=lg&gt; &lt;img hidefocus=true src=//www.baidu.com/img/bd_logo1.png width=270 height=129&gt; &lt;/div&gt; &lt;form id=form name=f action=//www.baidu.com/s class=fm&gt; &lt;input type=hidden name=bdorz_come value=1&gt; &lt;input type=hidden name=ie value=utf-8&gt; &lt;input </span></span> <span class="giallo-l"><span class="z-support z-function z-builtin">...</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_8#</span><span class="z-source"> </span></span></code></pre><h4 id="1-9">1.9</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.9: 修改fetch打印出HTTP协议的状态码，可以从resp.Status变量得到该状态码。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// Fetch prints the content found at a URL.</span></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;io&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;net/http&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> url</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">1</span><span class="z-source">:</span><span class="z-punctuation">] {</span></span> <span class="giallo-l"><span class="z-source"> resp</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> http</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Get</span><span class="z-punctuation">(</span><span class="z-source">url</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> err </span><span class="z-keyword z-operator">!=</span><span class="z-source"> nil </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stderr</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;fetch: %v</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> os</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Exit</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> b</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> io</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">ReadAll</span><span class="z-punctuation">(</span><span class="z-source">resp</span><span class="z-punctuation">.</span><span class="z-source">Body</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> resp</span><span class="z-punctuation">.</span><span class="z-source">Body</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Close</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-source"> err </span><span class="z-keyword z-operator">!=</span><span class="z-source"> nil </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">os</span><span class="z-punctuation">.</span><span class="z-source">Stderr</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;fetch: reading %s: %v</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> url</span><span class="z-punctuation">,</span><span class="z-source"> err</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> os</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Exit</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Printf</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;%s&quot;</span><span class="z-punctuation">,</span><span class="z-source"> b</span><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source"> status</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> resp</span><span class="z-punctuation">.</span><span class="z-source">Status</span><span class="z-punctuation z-definition z-comment z-comment"> // 获取状态码</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Println</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;Status: &quot;</span><span class="z-punctuation">,</span><span class="z-source"> status</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 打印状态码</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_9#</span><span class="z-string"> ./a.out https://www.baidu.com</span></span> <span class="giallo-l"><span class="z-keyword z-operator">&lt;!</span><span class="z-entity z-name z-function">DOCTYPE</span><span class="z-string"> htm</span><span class="z-source">l</span><span class="z-keyword z-operator">&gt;</span></span> <span class="giallo-l"><span class="z-keyword z-operator">&lt;!</span><span class="z-entity z-name z-function">--STATUS</span><span class="z-string"> OK-</span><span class="z-source">-&gt;&lt;</span><span class="z-string">htm</span><span class="z-source">l</span><span class="z-keyword z-operator">&gt; &lt;</span><span class="z-string">hea</span><span class="z-source">d&gt;&lt;</span><span class="z-string">meta http-equiv=content-type content=text/html</span><span class="z-punctuation">;</span><span class="z-source">charset</span><span class="z-keyword z-operator">=</span><span class="z-string">utf-8</span><span class="z-source">&gt;&lt;</span><span class="z-string">meta</span><span class="z-source"> http-equiv</span><span class="z-keyword z-operator">=</span><span class="z-string">X-UA-Compatible</span><span class="z-source"> content</span><span class="z-keyword z-operator">=</span><span class="z-source">IE</span><span class="z-keyword z-operator">=</span><span class="z-string">Edge</span><span class="z-source">&gt;&lt;</span><span class="z-string">meta</span><span class="z-source"> content</span><span class="z-keyword z-operator">=</span><span class="z-string">always</span><span class="z-source"> name</span><span class="z-keyword z-operator">=</span><span class="z-string">referrer</span><span class="z-source">&gt;&lt;</span><span class="z-string">link</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-support z-function z-builtin">...</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">Status:</span><span class="z-constant z-numeric"> 200</span><span class="z-string"> OK</span></span> <span class="giallo-l"><span class="z-source"> </span></span></code></pre><h4 id="1-10">1.10</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.10： 找一个数据量比较大的网站，用本小节中的程序调研网站的缓存</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 策略，对每个URL执行两遍请求，查看两次时间是否有较大的差别，并且每次获</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 取到的响应内容是否一致，修改本节中的程序，将响应结果输出到文件，以便于</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 进行对比。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// Fetchall fetches URLs in parallel and reports their times and sizes.</span></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;io&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;net/http&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;os&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;time&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-source"> start</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> time</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Now</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-source"> ch</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> make</span><span class="z-punctuation">(</span><span class="z-source">chan string</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // 新键通道（用于在routine之间传输数据）</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> _</span><span class="z-punctuation">,</span><span class="z-source"> url</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> range os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">1</span><span class="z-source">:</span><span class="z-punctuation">] {</span></span> <span class="giallo-l"><span class="z-source"> go</span><span class="z-entity z-name z-function"> fetch</span><span class="z-punctuation">(</span><span class="z-source">url</span><span class="z-punctuation">,</span><span class="z-source"> ch</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // start a goroutine</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> range os</span><span class="z-punctuation">.</span><span class="z-source">Args</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">1</span><span class="z-source">:</span><span class="z-punctuation">] {</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Println</span><span class="z-punctuation">(</span><span class="z-keyword z-operator">&lt;-</span><span class="z-source">ch</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // receive from channel ch</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Printf</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;%.2fs elapsed</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> time</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Since</span><span class="z-punctuation">(</span><span class="z-source">start</span><span class="z-punctuation">).</span><span class="z-entity z-name z-function">Seconds</span><span class="z-punctuation">())</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> fetch</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">url</span><span class="z-variable z-parameter"> string</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> ch chan</span><span class="z-punctuation">&lt;</span><span class="z-keyword z-operator">-</span><span class="z-entity z-name z-type"> string</span><span class="z-source">) {</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> start</span><span class="z-source"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> time.</span><span class="z-entity z-name z-type">Now</span><span class="z-source">()</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> resp</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> err</span><span class="z-source"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> http.</span><span class="z-entity z-name z-type">Get</span><span class="z-source">(</span><span class="z-entity z-name z-type">url</span><span class="z-source">)</span></span> <span class="giallo-l"><span class="z-source"> if</span><span class="z-entity z-name z-type"> err</span><span class="z-keyword z-operator"> !=</span><span class="z-entity z-name z-type"> nil</span><span class="z-source"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> ch</span><span class="z-punctuation"> &lt;</span><span class="z-keyword z-operator">-</span><span class="z-source"> fmt.</span><span class="z-entity z-name z-type">Sprint</span><span class="z-source">(</span><span class="z-entity z-name z-type">err</span><span class="z-source">)</span><span class="z-punctuation z-definition z-comment z-comment"> // send to channel ch</span></span> <span class="giallo-l"><span class="z-source"> return</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // 创建新文件（以时间戳命名）</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> fileName</span><span class="z-source"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> fmt.</span><span class="z-entity z-name z-type">Sprintf</span><span class="z-source">(</span><span class="z-punctuation z-definition z-string z-string">&quot;%v.txt&quot;</span><span class="z-punctuation">,</span><span class="z-source"> start.</span><span class="z-entity z-name z-type">Nanosecond</span><span class="z-source">())</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> file</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> err</span><span class="z-source"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> os.</span><span class="z-entity z-name z-type">Create</span><span class="z-source">(</span><span class="z-entity z-name z-type">fileName</span><span class="z-source">) </span></span> <span class="giallo-l"><span class="z-source"> if</span><span class="z-entity z-name z-type"> err</span><span class="z-keyword z-operator"> !=</span><span class="z-entity z-name z-type"> nil</span><span class="z-source"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> ch</span><span class="z-punctuation"> &lt;</span><span class="z-keyword z-operator">-</span><span class="z-source"> fmt.</span><span class="z-entity z-name z-type">Sprint</span><span class="z-source">(</span><span class="z-entity z-name z-type">err</span><span class="z-source">)</span></span> <span class="giallo-l"><span class="z-source"> return</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // 将响应结果保存至文件中</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> nbytes</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> err</span><span class="z-source"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> io.</span><span class="z-entity z-name z-type">Copy</span><span class="z-source">(</span><span class="z-entity z-name z-type">file</span><span class="z-punctuation">,</span><span class="z-source"> resp.</span><span class="z-entity z-name z-type">Body</span><span class="z-source">)</span></span> <span class="giallo-l"><span class="z-source"> resp.Body.</span><span class="z-entity z-name z-type">Close</span><span class="z-source">()</span><span class="z-punctuation z-definition z-comment z-comment"> // don&#39;t leak resources</span></span> <span class="giallo-l"><span class="z-source"> file.</span><span class="z-entity z-name z-type">Close</span><span class="z-source">()</span><span class="z-punctuation z-definition z-comment z-comment"> // 关闭文件</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source"> if</span><span class="z-entity z-name z-type"> err</span><span class="z-keyword z-operator"> !=</span><span class="z-entity z-name z-type"> nil</span><span class="z-source"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> ch</span><span class="z-punctuation"> &lt;</span><span class="z-keyword z-operator">-</span><span class="z-source"> fmt.</span><span class="z-entity z-name z-type">Sprintf</span><span class="z-source">(</span><span class="z-punctuation z-definition z-string z-string">&quot;while reading %s: %v&quot;</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> url</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> err</span><span class="z-source">)</span></span> <span class="giallo-l"><span class="z-source"> return</span></span> <span class="giallo-l"><span class="z-source"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> secs</span><span class="z-source"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> time.</span><span class="z-entity z-name z-type">Since</span><span class="z-source">(</span><span class="z-entity z-name z-type">start</span><span class="z-source">).</span><span class="z-entity z-name z-type">Seconds</span><span class="z-source">()</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> ch</span><span class="z-punctuation"> &lt;</span><span class="z-keyword z-operator">-</span><span class="z-source"> fmt.</span><span class="z-entity z-name z-type">Sprintf</span><span class="z-source">(</span><span class="z-punctuation z-definition z-string z-string">&quot;%.2fs %7d %s&quot;</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> secs</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> nbytes</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> url</span><span class="z-source">)</span></span> <span class="giallo-l"><span class="z-source">}</span></span> <span class="giallo-l"></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_10#</span><span class="z-string"> go build -o a.out</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_10#</span><span class="z-string"> ./a.out https://www.baidu.com https://www.baidu.com</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0.08s</span><span class="z-constant z-numeric"> 2443</span><span class="z-string"> https://www.baidu.com</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0.08s</span><span class="z-constant z-numeric"> 2443</span><span class="z-string"> https://www.baidu.com</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0.08s</span><span class="z-string"> elapsed</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_10#</span><span class="z-string"> ls</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">708404000.txt</span><span class="z-string"> 708408000.txt a.out main.go</span></span></code></pre><h4 id="1-11">1.11</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.11： 在fetchall中尝试使用长一些的参数列表，比如使用在alexa.com的上百万网站里排名靠前的。</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 如果一个网站没有回应，程序将采取怎样的行为？（Section8.9 描述了在这种情况下的应对机制）。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 答：没有回应程序会一直等待。</span></span></code></pre><h4 id="1-12">1.12</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 练习 1.12: 修改Lissajour服务，从URL读取变量，比如你可以访问 http://localhost:8000/?cycles=20 </span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 这个URL，这样访问可以将程序里的cycles默认的5修改为20。字符串转换为数字可以调用strconv.Atoi函数。你</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// 可以在godoc里查看</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// Server2 is a minimal &quot;echo&quot; and counter server.</span></span> <span class="giallo-l"><span class="z-source">package main</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">import </span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;fmt&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;log&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;net/http&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;sync&quot;</span><span class="z-punctuation z-definition z-comment z-comment"> // 同步</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;io&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;math/rand&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image/color&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;image/gif&quot;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-string z-string"> &quot;math&quot;</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">var mu sync</span><span class="z-punctuation">.</span><span class="z-source">Mutex</span></span> <span class="giallo-l"><span class="z-source">var count</span><span class="z-storage z-type"> int</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">var palette </span><span class="z-keyword z-operator">=</span><span class="z-punctuation"> []</span><span class="z-source">color.Color</span><span class="z-punctuation">{</span><span class="z-source">color</span><span class="z-punctuation">.</span><span class="z-source">White</span><span class="z-punctuation">,</span><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">Black</span><span class="z-punctuation">,</span><span class="z-source"> color</span><span class="z-punctuation">.</span><span class="z-source">RGBA</span><span class="z-punctuation">{</span><span class="z-keyword">0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">00</span><span class="z-punctuation">,</span><span class="z-keyword"> 0x</span><span class="z-constant z-numeric">ff</span><span class="z-punctuation">}}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier">const</span><span class="z-punctuation"> (</span></span> <span class="giallo-l"><span class="z-source"> whiteIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-definition z-comment z-comment"> // first color in palette</span></span> <span class="giallo-l"><span class="z-source"> blackIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation z-definition z-comment z-comment"> // next color in palette</span></span> <span class="giallo-l"><span class="z-source"> greenIndex </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 2</span><span class="z-punctuation z-definition z-comment z-comment"> // 绿色</span></span> <span class="giallo-l"><span class="z-punctuation">)</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">() {</span></span> <span class="giallo-l"><span class="z-source"> http</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">HandleFunc</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;/&quot;</span><span class="z-punctuation">,</span><span class="z-source"> handler</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> http</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">HandleFunc</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;/count&quot;</span><span class="z-punctuation">,</span><span class="z-source"> counter</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> http</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">HandleFunc</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;/lissajous&quot;</span><span class="z-punctuation">,</span><span class="z-entity z-name z-function"> func</span><span class="z-punctuation">(</span><span class="z-source">w http</span><span class="z-punctuation">.</span><span class="z-source">ResponseWriter</span><span class="z-punctuation">,</span><span class="z-source"> r </span><span class="z-keyword z-operator">*</span><span class="z-source">http</span><span class="z-punctuation">.</span><span class="z-source">Request</span><span class="z-punctuation">)</span><span class="z-source"> {</span><span class="z-punctuation z-definition z-comment z-comment"> // 添加lissajous访问接口</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> lissajous</span><span class="z-punctuation">(</span><span class="z-source">w</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> }</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> log</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fatal</span><span class="z-punctuation">(</span><span class="z-source">http</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">ListenAndServe</span><span class="z-punctuation">(</span><span class="z-punctuation z-definition z-string z-string">&quot;localhost:8000&quot;</span><span class="z-punctuation">,</span><span class="z-source"> nil</span><span class="z-punctuation">))</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// handler echoes the Path component of the requested URL.</span></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> handler</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">w http</span><span class="z-source">.</span><span class="z-variable z-parameter">ResponseWriter</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> r</span><span class="z-storage z-modifier"> *</span><span class="z-entity z-name z-type">http</span><span class="z-source">.</span><span class="z-variable z-parameter">Request</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> mu</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Lock</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-source"> count</span><span class="z-keyword z-operator">++</span></span> <span class="giallo-l"><span class="z-source"> mu</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Unlock</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">w</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;URL.Path = %q</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> r</span><span class="z-punctuation">.</span><span class="z-source">URL</span><span class="z-punctuation">.</span><span class="z-source">Path</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// counter echoes the number of calls so far.</span></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> counter</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">w http</span><span class="z-source">.</span><span class="z-variable z-parameter">ResponseWriter</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> r</span><span class="z-storage z-modifier"> *</span><span class="z-entity z-name z-type">http</span><span class="z-source">.</span><span class="z-variable z-parameter">Request</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> mu</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Lock</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-source"> fmt</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Fprintf</span><span class="z-punctuation">(</span><span class="z-source">w</span><span class="z-punctuation">,</span><span class="z-punctuation z-definition z-string z-string"> &quot;Count %d</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">,</span><span class="z-source"> count</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> mu</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Unlock</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-type">func</span><span class="z-entity z-name z-function"> lissajous</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">out io</span><span class="z-source">.</span><span class="z-variable z-parameter">Writer</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-punctuation"> (</span></span> <span class="giallo-l"><span class="z-source"> cycles </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 5</span><span class="z-punctuation z-definition z-comment z-comment"> // number of complete x oscillator revolutions</span></span> <span class="giallo-l"><span class="z-source"> res </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.001</span><span class="z-punctuation z-definition z-comment z-comment"> // angular resolution</span></span> <span class="giallo-l"><span class="z-source"> size </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 100</span><span class="z-punctuation z-definition z-comment z-comment"> // image canvas covers [-size..+size]</span></span> <span class="giallo-l"><span class="z-source"> nframes </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 64</span><span class="z-punctuation z-definition z-comment z-comment"> // number of animation frames</span></span> <span class="giallo-l"><span class="z-source"> delay </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 8</span><span class="z-punctuation z-definition z-comment z-comment"> // delay between frames in 10ms units</span></span> <span class="giallo-l"><span class="z-punctuation"> )</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source"> freq</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> rand</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Float64</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> *</span><span class="z-constant z-numeric"> 3.0</span><span class="z-punctuation z-definition z-comment z-comment"> // relative frequency of y oscillator</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> gif</span><span class="z-punctuation">.</span><span class="z-source">GIF</span><span class="z-punctuation">{</span><span class="z-source">LoopCount</span><span class="z-punctuation">:</span><span class="z-source"> nframes</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-source"> phase</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.0</span><span class="z-punctuation z-definition z-comment z-comment"> // phase difference</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> i</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> nframes</span><span class="z-punctuation">;</span><span class="z-source"> i</span><span class="z-keyword z-operator">++</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> rect</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> image</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Rect</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 2</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 2</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> img</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> image</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">NewPaletted</span><span class="z-punctuation">(</span><span class="z-source">rect</span><span class="z-punctuation">,</span><span class="z-source"> palette</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-source"> t</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0.0</span><span class="z-punctuation">;</span><span class="z-source"> t </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> cycles</span><span class="z-keyword z-operator">*</span><span class="z-constant z-numeric">2</span><span class="z-keyword z-operator">*</span><span class="z-source">math</span><span class="z-punctuation">.</span><span class="z-source">Pi</span><span class="z-punctuation">;</span><span class="z-source"> t </span><span class="z-keyword z-operator">+=</span><span class="z-source"> res </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> x</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> math</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Sin</span><span class="z-punctuation">(</span><span class="z-source">t</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> y</span><span class="z-punctuation"> :</span><span class="z-keyword z-operator">=</span><span class="z-source"> math</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">Sin</span><span class="z-punctuation">(</span><span class="z-source">t</span><span class="z-keyword z-operator">*</span><span class="z-source">freq </span><span class="z-keyword z-operator">+</span><span class="z-source"> phase</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> img</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">SetColorIndex</span><span class="z-punctuation">(</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-storage z-type">int</span><span class="z-punctuation">(</span><span class="z-source">x</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">0.5</span><span class="z-punctuation">),</span><span class="z-source"> size</span><span class="z-keyword z-operator">+</span><span class="z-storage z-type">int</span><span class="z-punctuation">(</span><span class="z-source">y</span><span class="z-keyword z-operator">*</span><span class="z-source">size</span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric">0.5</span><span class="z-punctuation">),</span></span> <span class="giallo-l"><span class="z-source"> blackIndex</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> phase </span><span class="z-keyword z-operator">+=</span><span class="z-constant z-numeric"> 0.1</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation">.</span><span class="z-source">Delay</span><span class="z-keyword z-operator"> =</span><span class="z-entity z-name z-function"> append</span><span class="z-punctuation">(</span><span class="z-source">anim</span><span class="z-punctuation">.</span><span class="z-source">Delay</span><span class="z-punctuation">,</span><span class="z-source"> delay</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> anim</span><span class="z-punctuation">.</span><span class="z-source">Image</span><span class="z-keyword z-operator"> =</span><span class="z-entity z-name z-function"> append</span><span class="z-punctuation">(</span><span class="z-source">anim</span><span class="z-punctuation">.</span><span class="z-source">Image</span><span class="z-punctuation">,</span><span class="z-source"> img</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> gif</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">EncodeAll</span><span class="z-punctuation">(</span><span class="z-source">out</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> &amp;</span><span class="z-source">anim</span><span class="z-punctuation">)</span><span class="z-punctuation z-definition z-comment z-comment"> // NOTE: ignoring encoding errors</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">sy1_12#</span><span class="z-string"> go build -o a.out</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sy1_12#</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span></code></pre> <p><img src="/csdn/13_3.png" alt="" /></p> <h3 id="zong-jie">总结</h3> <ul> <li>Go语言是一门现代化的语言，从其方便的工具链、简洁的语法规则可得一瞥。</li> </ul> 2024-11-26T00:00:00+00:00 2024-11-26T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/12-valid-anagram/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定两个字符串 <code>s</code> 和 <code>t</code> ，编写一个函数来判断 <code>t</code> 是否是 <code>s</code> 的字母异位词。字母异位词是指通过重新排列不同单词或短语的字母而形成的单词或短语，并使用所有原字母一次。</p> <p>原题链接： <a rel="external" href="https://leetcode.cn/problems/valid-anagram/">242. 有效的字母异位词</a></p> <hr /> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-pai-xu-fa">1 排序法</h3> <h4 id="fen-xi">分析</h4> <p>按照字母异位词的定义可知：如果两个字符串属于字母异位词，那么将两者排序后，其字符串必相同。</p> <h4 id="dai-ma">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> isAnagram</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">string</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> string</span><span class="z-variable z-parameter"> t</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> sort</span><span class="z-punctuation">(</span><span class="z-source">s</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">begin</span><span class="z-punctuation">(),</span><span class="z-source"> s</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">end</span><span class="z-punctuation">());</span><span class="z-punctuation z-definition z-comment z-comment"> // 排序s</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> sort</span><span class="z-punctuation">(</span><span class="z-source">t</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">begin</span><span class="z-punctuation">(),</span><span class="z-source"> t</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">end</span><span class="z-punctuation">());</span><span class="z-punctuation z-definition z-comment z-comment"> // 排序t</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> s </span><span class="z-keyword z-operator">==</span><span class="z-source"> t</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 比较s和t是否相等</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(nlogn)</code> ，即快速排序长度为 <code>n</code> 的字符串的时间复杂度。</p> </li> <li> <p>空间复杂度： <code>O(logn)</code> ，即快速排序长度为 <code>n</code> 的字符串的空间复杂度。</p> </li> </ul> <h3 id="2ha-xi-biao">2哈希表</h3> <h4 id="fen-xi-1">分析</h4> <p>对比字符串中每个字母的使用次数，同样可以判断二者是否是字母异位词。正好可以字母为键、使用次数为值的哈希表作为数据结构。</p> <p>因为字母仅有 <code>26</code> 个小写字母组成，不妨将其映射到数值 <code>0～25</code> ，这样的话可直接使用数组存储哈希表。</p> <h4 id="dai-ma-1">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> isAnagram</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">string</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> string</span><span class="z-variable z-parameter"> t</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> sLen </span><span class="z-keyword z-operator">=</span><span class="z-source"> s</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 获取字符串s的长度</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> tLen </span><span class="z-keyword z-operator">=</span><span class="z-source"> t</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 获取字符串t的长度</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">sLen </span><span class="z-keyword z-operator">!=</span><span class="z-source"> tLen</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 如果两者长度不一致</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 直接返回false</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> table</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">26</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> =</span><span class="z-punctuation"> {</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">};</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化哈希表为0</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> sLen</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历字符串s</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">table</span><span class="z-punctuation">[</span><span class="z-source">s</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> -</span><span class="z-punctuation z-definition z-string z-string"> &#39;a&#39;</span><span class="z-punctuation">];</span><span class="z-punctuation z-definition z-comment z-comment"> // 构建哈希表</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> tLen</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历字符串t</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">--</span><span class="z-source">table</span><span class="z-punctuation">[</span><span class="z-source">t</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> -</span><span class="z-punctuation z-definition z-string z-string"> &#39;a&#39;</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> &lt;</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // “析构”哈希表，且如果发现计数小于0（说明字母出现次数不匹配）</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回false</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-true"> true</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回true</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du-1">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(n)</code> ，遍历长度为 <code>n</code> 的字符串.</p> </li> <li> <p>空间复杂度： <code>O(26)</code> ， <code>26</code> 个小写字母</p> </li> </ul> <hr /> <h2 id="san-zong-jie">三 总结</h2> <ul> <li>使用特定字作为键的哈希表可以转换为用数组存储。</li> </ul> <hr /> 2024-11-19T00:00:00+00:00 2024-11-19T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/11-ransom-note/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定两个字符串： <code>ransomNote</code> 和 <code>magazine</code> ，判断 <code>ransomNote</code> 能不能由 <code>magazine</code> 里面的字符构成。其中 <code>magazine</code> 中的每个字符只能在 <code>ransomNote</code> 中使用一次，且 <code>ransomNote</code> 和 <code>magazine</code> 均由小写字母组成。</p> <p>原题链接： <a rel="external" href="https://leetcode.cn/problems/ransom-note/">383. 赎金信</a></p> <hr /> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1ha-xi-biao">1哈希表</h3> <h4 id="fen-xi">分析</h4> <p>判断字符串ransomNote是否能由另一字符串magazine中的元素构成，只需要满足字符串magazine中每个元素的次数都大于等于ransomNote中相同元素的统计次数即可。所以该问题的关键是统计字符串所包含的全部元素以及元素的出现次数，并以一种合理的方式存储它们。</p> <p>已知元素只有小写字母组成，次数可以直接用整数表示，使用以字符为键、整形为值的哈希表存储，不管是构建还是使用都十分方便。</p> <p>易知：字符串ransomNote的必须小于字符串magazine的长度。</p> <h4 id="dai-ma">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> canConstruct</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">string</span><span class="z-variable z-parameter"> ransomNote</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> string</span><span class="z-variable z-parameter"> magazine</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> ransomNote</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">(),</span><span class="z-source"> m </span><span class="z-keyword z-operator">=</span><span class="z-source"> magazine</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 获取字符串长度</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">n </span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> m</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // ransomNote长度大于magazine长度</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 不满足条件，直接返回false</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> unordered_map</span><span class="z-keyword z-operator">&lt;</span><span class="z-storage z-type">char</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-keyword z-operator">&gt;</span><span class="z-entity z-name z-function"> table</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">);</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化哈希表为零（零表示该字符不存在）</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> m</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历magazine，构建哈希表</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">table</span><span class="z-punctuation">[</span><span class="z-source">magazine</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">)];</span><span class="z-punctuation z-definition z-comment z-comment"> // 该元素对应次数累加</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历ransomNote字符串</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">--</span><span class="z-source">table</span><span class="z-punctuation">[</span><span class="z-source">ransomNote</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">)]</span><span class="z-keyword z-operator"> &lt;</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 出现一次字符，对应哈希表减一</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 出现小于0（代表字符不够），直接返回false</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-true"> true</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回true</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(m+n)</code> ，即两个字符串的长度和</p> </li> <li> <p>空间复杂度： <code>O(26)</code> ，即 <code>26</code> 个小写英文字符</p> </li> </ul> <h3 id="2shu-zu-ha-xi-biao">2数组哈希表</h3> <h4 id="fen-xi-1">分析</h4> <p>已知哈希表中键只由 <code>26</code> 个小写英文字母 <code>a~z</code> 组成，易将其映射到 <code>0~25</code> ，因此可以用数组作为哈希表的实现方式。</p> <h4 id="dai-ma-1">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> canConstruct</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">string</span><span class="z-variable z-parameter"> ransomNote</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> string</span><span class="z-variable z-parameter"> magazine</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> table</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">26</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> =</span><span class="z-punctuation"> {</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">};</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化数组哈希表为0</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> ransomNote</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">(),</span><span class="z-source"> m </span><span class="z-keyword z-operator">=</span><span class="z-source"> magazine</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 获取两字符串长度</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">n </span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> m</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // ransomNote长度大于magazine长度</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 不满足条件，直接返回false</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> m</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历magazine，构建数组哈希表</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">table</span><span class="z-punctuation">[</span><span class="z-source">magazine</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> -</span><span class="z-punctuation z-definition z-string z-string"> &#39;a&#39;</span><span class="z-punctuation">];</span><span class="z-punctuation z-definition z-comment z-comment"> // 数组哈希表对应元素值加1</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历ransomNote</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">--</span><span class="z-source">table</span><span class="z-punctuation">[</span><span class="z-source">ransomNote</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> -</span><span class="z-punctuation z-definition z-string z-string"> &#39;a&#39;</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> &lt;</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 数组哈希表对应元素减1</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 出现小于0，直接返回false</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-true"> true</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回true</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du-1">复杂度</h4> <p>同上</p> <hr /> <h2 id="san-zong-jie">三 总结</h2> <ul> <li>哈希表并不一定要使用专门的数据结构，也可以用数组实现。</li> </ul> <hr /> 2024-11-12T00:00:00+00:00 2024-11-12T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/10-h-index/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定一个整数数组 <code>citations</code> ，其中 <code>citations[i]</code> 代表研究者的第 <code>i</code> 篇论文被引用的次数。计算并返回该研究者的 <code>h</code> 指数。</p> <p><code>h</code> 代表“高引用次数“，一名科研人员的 <code>h</code> 指数是指他（她）至少发表了 <code>h</code> 篇论文，且至少有 <code>h</code> 篇论文的被引用次数大于等于 <code>h</code> 。如果 <code>h</code> 有多种可能值，那 <code>h</code> 指数是其中最大的那个。</p> <p><a rel="external" href="https://leetcode.cn/problems/h-index/">274. H 指数</a></p> <hr /> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-bao-li-fa">1 暴力法</h3> <h4 id="fen-xi">分析</h4> <p>因为 <code>h</code> 指数一定小于等于论文数，因此只要穷举所有的论文数，就一定能找到 <code>h</code> 指数。</p> <p>具体做法如下：使用两层循环，第一层循环尝试所有可能的引用数（最大为论文数）作为 <code>h</code> 指数的候选值，第二层循环遍历数组，记录引用次数大于 <code>h</code> 的元素个数即论文数，找到最大满足「论文数大于引用数」的值，即为 <code>h</code> 值。</p> <h4 id="dai-ma">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> hIndex</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> citations</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> citations</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 转储数组大小</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> refCnt </span><span class="z-keyword z-operator">=</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化最高引用数为数组大小（论文篇数）</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">refCnt</span><span class="z-keyword z-operator">--</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 尝试所有可能的引用次数（从高到低）</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> paperCnt </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化高引用论文数为0</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> j </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> j </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">j</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历数组</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">citations</span><span class="z-punctuation">[</span><span class="z-source">j</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> &gt;=</span><span class="z-source"> refCnt</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 记录引用次数高于指定次数的论文</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">paperCnt</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">paperCnt </span><span class="z-keyword z-operator">&gt;=</span><span class="z-source"> refCnt</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 如果首次找到（即最高）满足条件引用次数，跳出循环</span></span> <span class="giallo-l"><span class="z-keyword"> break</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> refCnt</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回引用次数</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(n^2)</code> ，遍历长度为 <code>n</code> 的数组嵌套遍历两次。</p> </li> <li> <p>空间复杂度： <code>O(1)</code> ，只使用常数个变量。</p> </li> </ul> <h3 id="2-pai-xu">2 排序</h3> <h4 id="fen-xi-1">分析</h4> <p><code>h</code> 指数代表“高引用次数”，不妨将代表论文引用次数的数组 <code>citations</code> 排序。此时，只要找到一个位置的引用次数，大于其之后的元素个数（论文篇数），该引用次数即为 <code>h</code> 指数。</p> <p>因为需要计算数组中某一位置元素后的元素个数，反向遍历比较合适，具体做法如下：初始化一变量为0，用于存储元素个数，反向遍历数组，在每次访问完一元素时，累加该变量。</p> <h4 id="dai-ma-1">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> hIndex</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> citations</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> sort</span><span class="z-punctuation">(</span><span class="z-source">citations</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">begin</span><span class="z-punctuation">(),</span><span class="z-source"> citations</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">end</span><span class="z-punctuation">());</span><span class="z-punctuation z-definition z-comment z-comment"> // 排序</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> citations</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 转储数组打下</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> h </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化h指数为0</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-source"> n </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&gt;=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> --</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 反向遍历排序后的数组</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">citations</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> &gt;</span><span class="z-source"> h</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 如果引用次数大于h指数</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">h</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // h指数累加</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> h</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回h指数</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du-1">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(nlogn)</code> ，即排序长度为 <code>n</code> 数组的时间复杂度。</p> </li> <li> <p>空间复杂度： <code>O(n)</code> ，即排序长度为 <code>n</code> 数组的空间复杂度。</p> </li> </ul> <h3 id="3-ji-shu-pai-xu">3 计数排序</h3> <blockquote> <p>计数排序：将原数组以新的计数数组方式存储，以达到排序效果。其中计数数组是：数组下标为元素值，数组元素为原数组元素出现的次数。因为数组下标（此时还表示原数组元素）本就是排序好的，因此也可以看作是一种排序。新的数组大小也就是原数组中最大的值，因此计数排序一般用于整数数组，且最大值已知。</p> </blockquote> <h4 id="fen-xi-2">分析</h4> <p>计数排序的关键在于找到原数组的最大值，以方便构建计数数组。由题意知： <code>h</code> 指数不会大于研究者的论文篇数 <code>n</code> ，因此所有引用次数大于 <code>n</code> 的论文都可以存储在第 <code>n+1</code> 个位置。也就是说计数数组大小为 <code>n+1</code> 。</p> <p>当获得按计数排序的数组后，反向遍历，累加论文篇数（数组元素），找到首次论文篇数大于等于引用数（数组下标）的下标位置，此时的下标值即为 <code>h</code> 指数。</p> <h4 id="dai-ma-2">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> hIndex</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> citations</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> citations</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 转储数组大小</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> cnt </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化计数和为0</span></span> <span class="giallo-l"><span class="z-source"> vector</span><span class="z-keyword z-operator">&lt;</span><span class="z-storage z-type">int</span><span class="z-keyword z-operator">&gt;</span><span class="z-entity z-name z-function"> counter</span><span class="z-punctuation">(</span><span class="z-source">n </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">);</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化计数数组为{0}，用于存储按计数排序后的数组</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历数组，构建计数数组</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">citations</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> &gt;</span><span class="z-source"> n</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 引用次数大于n，按照次数为n记录</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">counter</span><span class="z-punctuation">[</span><span class="z-source">n</span><span class="z-punctuation">];</span><span class="z-punctuation z-definition z-comment z-comment"> // </span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">counter</span><span class="z-punctuation">[</span><span class="z-source">citations</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">)];</span><span class="z-punctuation z-definition z-comment z-comment"> // 否则按照实际次数记录</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&gt;=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> --</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 反向遍历计数数组</span></span> <span class="giallo-l"><span class="z-source"> cnt </span><span class="z-keyword z-operator">+=</span><span class="z-source"> counter</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">i</span><span class="z-punctuation">);</span><span class="z-punctuation z-definition z-comment z-comment"> // 累加当前引用次数下的论文篇数</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">cnt </span><span class="z-keyword z-operator">&gt;=</span><span class="z-source"> i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 论文篇数大于等于当前引用次数</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> i</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 找到h指数，返回结果</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 为找到h指数，返回0</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du-2">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(n)</code> ，遍历数组长度为 <code>n</code> 的 <code>citations</code> 数组一次，遍历数组长度为 <code>n+1</code> 的 <code>counter</code> 数组一次。</p> </li> <li> <p>空间复杂度： <code>O(n)</code> ，构建长度为 <code>n+1</code> 的数组 <code>counter</code> 。</p> </li> </ul> <hr /> <h2 id="san-zong-jie">三 总结</h2> <ul> <li>当排序能解决问题，且数组元素为整数值时，不妨考虑计数排序。</li> </ul> <hr /> 2024-11-11T00:00:00+00:00 2024-11-11T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/09-length-of-last-word/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定一个字符串 <code>s</code> ，由若干单词组成，单词前后有一些空格字符隔开。返回字符串中最后一个单词的长度。</p> <p><a rel="external" href="https://leetcode.cn/problems/length-of-last-word/">58. 最后一个单词的长度</a></p> <hr /> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-ni-xu-bian-li">1 逆序遍历</h3> <h4 id="fen-xi">分析</h4> <p>初始化最后一个单词长度 <code>length = 0</code> ，逆序遍历数组，累加 <code>length</code> ，直到找到第一个为空格字符的元素。此时 <code>length</code> 即为所求值。值得注意的是：字符串末尾可能含有空格字符，需先清除它们，再开始计数单词长度。</p> <h4 id="dai-ma">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> lengthOfLastWord</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">string</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> length </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> start </span><span class="z-keyword z-operator">=</span><span class="z-source"> s</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> -</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化最后一个单词长度为0，逆序下标为n-1</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">start </span><span class="z-keyword z-operator">&gt;=</span><span class="z-constant z-numeric"> 0</span><span class="z-keyword z-operator"> &amp;&amp;</span><span class="z-source"> s</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">start</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> ==</span><span class="z-punctuation z-definition z-string"> &#39; &#39;</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 如果存在末尾空格，清除它们（跳过）</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> --</span><span class="z-source">start</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新下标</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">start </span><span class="z-keyword z-operator">&gt;=</span><span class="z-constant z-numeric"> 0</span><span class="z-keyword z-operator"> &amp;&amp;</span><span class="z-source"> s</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">at</span><span class="z-punctuation">(</span><span class="z-source">start</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> !=</span><span class="z-punctuation z-definition z-string"> &#39; &#39;</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 循环直到找到空格字符</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">length</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 单词长度+1</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> --</span><span class="z-source">start</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新下标</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> length</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回单词长度</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du">复杂度</h4> <ul> <li> <p>时间复杂度： <code>O(n)</code> ，遍历（逆序）长度为 <code>n</code> 的数组一次。</p> </li> <li> <p>空间复杂度： <code>O(1)</code> ，常数个变量。</p> </li> </ul> <h2 id="san-zong-jie">三 总结</h2> <ul> <li>正序遍历不好解决问题时，不妨考虑逆序遍历。</li> </ul> <hr /> 2024-11-09T00:00:00+00:00 2024-11-09T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/01-majority-element/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>统计数组中出现次数大于「n/2」的元素，其中n为数组长度，你可以假设该类元素必存在。</p> <p>[ <a rel="external" href="https://leetcode.cn/problems/majority-element/">169. 多数元素</a> ]</p> <blockquote> <p>注意：「n/2」代表对算式 n/2 的结果向下取整，下同。</p> </blockquote> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1ha-xi-biao-fa">1哈希表法</h3> <h4 id="fen-xi">分析</h4> <p>题目要求统计出现次数大于「n/2」的元素，显而易见的方法是：统计所有元素出现的次数，找到其中大于「n/2」的元素。为了方便查找，使用以元素值为键、元素出现次数为值的哈希表作为数据结构。只要构建好哈希表后，目标元素就容易找出来了。</p> <h4 id="dai-ma">代码</h4> <ul> <li> <p>初始化以元素为键，以出现次数为值的哈希表</p> </li> <li> <p>遍历数组，将元素存放在哈希表中</p> </li> <li> <p>在遍历过程中，检查是否存在值大于「n/2」的元素，存在则返回该元素。</p> </li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> majorityElement</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> unordered_map</span><span class="z-keyword z-operator">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> table</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> size_t</span><span class="z-source"> len </span><span class="z-keyword z-operator">=</span><span class="z-source"> nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span></span> <span class="giallo-l"><span class="z-storage z-type"> size_t</span><span class="z-source"> num </span><span class="z-keyword z-operator">=</span><span class="z-source"> len </span><span class="z-keyword z-operator">/</span><span class="z-constant z-numeric"> 2</span><span class="z-punctuation">,</span><span class="z-source"> ret </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> len</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">++</span><span class="z-source">table</span><span class="z-punctuation">[</span><span class="z-source">nums</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]]</span><span class="z-keyword z-operator"> &gt;</span><span class="z-source"> num</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> ret </span><span class="z-keyword z-operator">=</span><span class="z-source"> nums</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">];</span></span> <span class="giallo-l"><span class="z-keyword"> break</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> ret</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span> <span class="giallo-l"></span></code></pre> <ul> <li>或者也可以在构建完成哈希表之后，遍历找到值最大的键（次数大于「n/2」肯定是最值），即为所需结果。</li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> majorityElement</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> unordered_map</span><span class="z-keyword z-operator">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> table</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> size_t</span><span class="z-source"> len </span><span class="z-keyword z-operator">=</span><span class="z-source"> nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span></span> <span class="giallo-l"><span class="z-storage z-type"> size_t</span><span class="z-source"> cnt </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> ret </span><span class="z-keyword z-operator">=</span><span class="z-source"> nums</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">];</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> len</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">table</span><span class="z-punctuation">[</span><span class="z-source">nums</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]];</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-modifier z-storage z-type">const auto</span><span class="z-keyword z-operator">&amp;</span><span class="z-source"> item </span><span class="z-punctuation">:</span><span class="z-source"> table</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">item</span><span class="z-punctuation">.</span><span class="z-source">second</span><span class="z-keyword z-operator"> &gt;</span><span class="z-source"> cnt</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> cnt </span><span class="z-keyword z-operator">=</span><span class="z-source"> item</span><span class="z-punctuation">.</span><span class="z-source">second</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> ret </span><span class="z-keyword z-operator">=</span><span class="z-source"> item</span><span class="z-punctuation">.</span><span class="z-source">first</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> ret</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h3 id="2-pai-xu-fa">2 排序法</h3> <h4 id="fen-xi-1">分析</h4> <p>将数组排序，因为结果元素值出现次数大于「n/2」，考虑最极端情况：结果值最大/最小（起始/终止）且结果值次数为「n/2」+1，其数组下标「n/2」的位置也为该结果值，不管数组大小是奇数还是偶数。</p> <h4 id="dai-ma-1">代码</h4> <ul> <li> <p>给数组排序</p> </li> <li> <p>访问下标「n/2」位置的元素值</p> </li> </ul> <pre class="giallo z-code"><code data-lang="c"><span class="giallo-l"><span class="z-source">class Solution </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source">public:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> majorityElement</span><span class="z-punctuation">(</span><span class="z-source">vector</span><span class="z-keyword z-operator">&lt;</span><span class="z-storage z-type">int</span><span class="z-keyword z-operator">&gt;&amp;</span><span class="z-source"> nums</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> sort</span><span class="z-punctuation">(</span><span class="z-source">nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">begin</span><span class="z-punctuation">(),</span><span class="z-source"> nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">end</span><span class="z-punctuation">());</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> nums</span><span class="z-punctuation">[</span><span class="z-source">nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> /</span><span class="z-constant z-numeric"> 2</span><span class="z-punctuation">];</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h2 id="san-zong-jie">三 总结</h2> <p>找到数据的特性，解决问题的方法也许很简单。比如方法2中提到排序法，是利用众数的特性，从而让我们可以快速找到目标元素。</p> 2024-11-09T00:00:00+00:00 2024-11-09T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/02-best-time-to-buy-and-sell-stock/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定一个数组，找到两个元素，使得后一个元素减去前一个元素的值最大，返回这个最大值。如果不存在则返回0。</p> <p><a rel="external" href="https://leetcode.cn/problems/best-time-to-buy-and-sell-stock/">121.买卖股票的最佳时机</a></p> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-bao-li-fa">1 暴力法</h3> <h4 id="fen-xi">分析</h4> <p>因为需要找到两个元素，很容易想到遍历两次数组的暴力法：第一层循环记录前一个元素下标，第二层循环记录后一个元素下标，找到二者差的最大值。</p> <h4 id="dai-ma">代码</h4> <ul> <li> <p>第一次遍历数组，用 <code>i</code> 记录前一个元素下标</p> </li> <li> <p>第二次遍历数组，用 <code>j</code> 记录后一个元素下标，且 <code>j</code> 直接从 <code>i + 1</code> 开始</p> </li> <li> <p>二者相减，保存相减后的最大值</p> </li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> maxProfit</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> prices</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> nums </span><span class="z-keyword z-operator">=</span><span class="z-source"> prices</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 数组长度</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> ret </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> cur</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回值（最大差值）和临时值</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> nums </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 第一层循环：记录前一个元素下标</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> j </span><span class="z-keyword z-operator">=</span><span class="z-source"> i </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-source"> j </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> nums</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">j</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 第二层循环：记录后一个元素下标</span></span> <span class="giallo-l"><span class="z-source"> cur </span><span class="z-keyword z-operator">=</span><span class="z-source"> prices</span><span class="z-punctuation">[</span><span class="z-source">j</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> -</span><span class="z-source"> prices</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">];</span><span class="z-punctuation z-definition z-comment z-comment"> // 计算二者差值</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">cur </span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> ret</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 与最大差值比较</span></span> <span class="giallo-l"><span class="z-source"> ret </span><span class="z-keyword z-operator">=</span><span class="z-source"> cur</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新最大差值</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> ret</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回结果</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre> <p>这里运用到了一个代码小技巧，因为最小值必为0（自己减自己），因此可令返回值默认为0，之后就可在两层循环中省去下标重复的地方。比如： <code>i &lt; nums - 1</code> 和 <code>j = i + 1</code> 。</p> <h3 id="2-wei-hu-zui-xiao-zhi">2 维护最小值</h3> <h4 id="fen-xi-1">分析</h4> <p>对于数组里任一元素来说，要想取得最大结果差值，其必须和出现在数组前面的最小值相减。因此可以维护一个最小值，用于跟当前数组元素比较。此时只用了一个循环。</p> <h4 id="dai-ma-1">代码</h4> <ul> <li> <p>记录首值为最小值，记录0为最大差值</p> </li> <li> <p>遍历数组除首值之外部分</p> </li> <li> <p>更新最大差值，更新最小值</p> </li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> maxProfit</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> prices</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> nums </span><span class="z-keyword z-operator">=</span><span class="z-source"> prices</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 数组长度</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> minPrice </span><span class="z-keyword z-operator">=</span><span class="z-source"> prices</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">],</span><span class="z-source"> maxProfit </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 最小值，最大差值</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> nums</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历数组</span></span> <span class="giallo-l"><span class="z-source"> maxProfit </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> max</span><span class="z-punctuation">(</span><span class="z-source">maxProfit</span><span class="z-punctuation">,</span><span class="z-source"> prices</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> -</span><span class="z-source"> minPrice</span><span class="z-punctuation">);</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新最大差值</span></span> <span class="giallo-l"><span class="z-source"> minPrice </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> min</span><span class="z-punctuation">(</span><span class="z-source">prices</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">],</span><span class="z-source"> msnPrice</span><span class="z-punctuation">);</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新最小值</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> maxProfit</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回结果值</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h2 id="san-zong-jie">三 总结</h2> <ol> <li> <p>暴力法用了两层循环，所以时间复杂度为 $0(n^2)$ ；只用了常数个变量，所以空间复杂度为 $0(1)$ 。因为时间复杂度高，无法通过时间限制测试。</p> </li> <li> <p>维护最小值法只用了单层循环，时间复杂度为 $0(n)$ ；只用了常数个变量，所以空间复杂度也为 $0(1)$ 。</p> </li> <li> <p>维护最小值也可以看作双指针法的变体，其中仍有一个指针用于遍历数组，但另一个记录下标的指针则变成了记录元素值的变量。</p> </li> </ol> 2024-11-09T00:00:00+00:00 2024-11-09T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/03-best-time-to-buy-and-sell-stock-ii/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定一个数组，查找数组中所有存在的元素对，使得元素对差值（后一个元素减去前一个的值）和最大。元素对之间不相交，求所有元素对的最大差值和。</p> <p><a rel="external" href="https://leetcode.cn/problems/best-time-to-buy-and-sell-stock-ii/">122. 买卖股票的最佳时机 II</a></p> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-tan-xin-fa">1 贪心法</h3> <h4 id="fen-xi">分析</h4> <p>直接找出所有最优元素对十分困难，不妨换种思路——找最小范围元素对。</p> <p>计算所有最小范围的元素对（即相邻元素，这是十分简单能找到的）的最优差值，累加这些差值即可得到最大差值和，所以关键是如何确保相邻元素差值最优。</p> <p>因为元素对可以只有一个元素，因此可以确保差值最小值必大于等于0，也就是说累加所有相邻元素的差值和0的较大者，即可获得最大差值和。</p> <h4 id="dai-ma">代码</h4> <ul> <li> <p>初始化最大差值和为0</p> </li> <li> <p>从第二个元素开始遍历数组</p> </li> <li> <p>比较相邻元素（当前元素值减去前面的元素值）和0的大小，将较大者累加入最大差值中去</p> </li> <li> <p>返回最大差值</p> </li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> maxProfit</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> prices</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> ret </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> len </span><span class="z-keyword z-operator">=</span><span class="z-source"> prices</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化最大差值和为0；记录数组大小（用于遍历）</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> len</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 从第二个元素开始循环（因为需要计算相邻元素差）</span></span> <span class="giallo-l"><span class="z-source"> ret </span><span class="z-keyword z-operator">+=</span><span class="z-entity z-name z-function"> max</span><span class="z-punctuation">(</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">,</span><span class="z-source"> prices</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> -</span><span class="z-source"> prices</span><span class="z-punctuation">[</span><span class="z-source">i </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">]);</span><span class="z-punctuation z-definition z-comment z-comment"> // 将相邻元素差与0中对较大者累加入最大差值</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> ret</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回最大差值和</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h3 id="2dong-tai-gui-hua">2动态规划</h3> <h4 id="fen-xi-1">分析</h4> <p>仍然考虑由局部最优推倒出全局最优。</p> <p>从数组的第一个元素开始，存在两种状态：一是可以将其作为元素对的起始、二是将其作为元素对的结束（后面将简记为起始状态和结束状态），同时记录两种状态下的解：起始状态解是0，终止状态解是当前元素值的负数（假定后面一定能找到一个元素与其组成元素对，因此解是负数）。</p> <p>对于下一个元素，其状态也可以是起始或结束，且只与前一个元素的状态有关，计算下一个元素解方法为：新状态结束解=max(旧状态结束解, 旧状态起始解 + 当前元素值)；新状态起始解=max(旧状态起始解, 旧状态结束解 - 当前元素值)，取max以确保局部最优。</p> <p>以此类推，直到运行至数组的最后一个元素，即可获得两种状态下各自的全局最优解（最大差值和）。</p> <p>因为最后为结束状态一定比起时状态差值和大，所以结果选结束状态更优。</p> <h4 id="dai-ma-1">代码</h4> <ul> <li> <p>初始化起始状态值和结束状态值</p> </li> <li> <p>遍历数组</p> </li> <li> <p>更新起始状态值和终止状态值</p> </li> <li> <p>返回最后元素结束状态下的值（最大差值和）</p> </li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> maxProfit</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> prices</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> prices</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 记录数组长度</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> dp0 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> dp1 </span><span class="z-keyword z-operator">= -</span><span class="z-source">prices</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">];</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化两种状态的最大差值和，0为结束状态，1为起始状态</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> newDp0</span><span class="z-punctuation">,</span><span class="z-source"> newDp1</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 临时变量，存放当前状态的最优解</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历数组</span></span> <span class="giallo-l"><span class="z-source"> newDp0 </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> max</span><span class="z-punctuation">(</span><span class="z-source">dp0</span><span class="z-punctuation">,</span><span class="z-source"> dp1 </span><span class="z-keyword z-operator">+</span><span class="z-source"> prices</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]);</span><span class="z-punctuation z-definition z-comment z-comment"> // 计算新结束状态值</span></span> <span class="giallo-l"><span class="z-source"> newDp1 </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> max</span><span class="z-punctuation">(</span><span class="z-source">dp1</span><span class="z-punctuation">,</span><span class="z-source"> dp0 </span><span class="z-keyword z-operator">-</span><span class="z-source"> prices</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]);</span><span class="z-punctuation z-definition z-comment z-comment"> // 计算新起始状态值</span></span> <span class="giallo-l"><span class="z-source"> dp0 </span><span class="z-keyword z-operator">=</span><span class="z-source"> newDp0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新</span></span> <span class="giallo-l"><span class="z-source"> dp1 </span><span class="z-keyword z-operator">=</span><span class="z-source"> newDp1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> dp0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回最后元素结束状态下的值</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre> <hr /> <h2 id="san-zong-jie">三 总结</h2> <ul> <li> <p>当局部最优能够推到出全局最优时，贪心算法是一种很好的思路方法。</p> </li> <li> <p>当程序出现多种状态，且状态前后相互影响时，可以尝试动态规划算法，其关键是找到状态和状态转变的方式。</p> </li> </ul> 2024-11-09T00:00:00+00:00 2024-11-09T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/04-jump-game/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定一个非负整数数组 <code>nums</code> ，你最初位于数组的首个位置，每个元素值代表你在该位置可以跳跃的最大长度。判断是否能从首个位置跳到最后一个位置。</p> <p><a rel="external" href="https://leetcode.cn/problems/jump-game/">55. 跳跃游戏</a></p> <hr /> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-tan-xin-fa">1 贪心法</h3> <h4 id="fen-xi">分析</h4> <p>对于数组内任意位置 <code>i</code> 的元素 <code>nums[i]</code> ，存在 <code>{i, i + 1, ... , i + nums[i]}</code> 个位置可以达。当跳跃到这些位置中的某一个的时候，在新的位置上又会产生一系列新的可达位置。也就是说，我们需要判断最后一个元素位置是否存在在这些位置、或这些位置的可达位置中。</p> <p>因为我们希望能达到的位置离数组最后一个位置越近越好，因此对于每一个位置的元素，我们都查找其最大的可达位置。如果所有的可达位置元素都不可达最后一个位置，那么数组也就无法从首个位置跳到最后一个位置。</p> <p>最初位于数组的首个位置，也就是说在最初的最远可达位置是 <code>0</code> 。</p> <h4 id="dai-ma">代码</h4> <ul> <li> <p>初始化可达最远位置为0</p> </li> <li> <p>遍历数组</p> </li> <li> <p>如果数组元素可达，更新最大可达位置</p> </li> <li> <p>检查是否可达数组最后一个位置</p> </li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> canJump</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 记录数组长度</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> maxIdx </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化可达最远位置为0</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历数组</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">i </span><span class="z-keyword z-operator">&lt;=</span><span class="z-source"> maxIdx</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 如果元素可达（可跳跃）</span></span> <span class="giallo-l"><span class="z-source"> maxIdx </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> max</span><span class="z-punctuation">(</span><span class="z-source">maxIdx</span><span class="z-punctuation">,</span><span class="z-source"> i </span><span class="z-keyword z-operator">+</span><span class="z-source"> nums</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]);</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新最大可达位置</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">maxIdx </span><span class="z-keyword z-operator">&gt;=</span><span class="z-source"> n </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 如果可达数组最后一个位置</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-true"> true</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回true</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历完数组仍不可达最后一个位置，返回false</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre> <ul> <li>也可将条件 <code>i &lt; n</code> 和 <code>i &lt;= maxIdx</code> 合并，循环只遍历到可达的最大范围。</li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> canJump</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> maxIdx </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;=</span><span class="z-source"> maxIdx</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> maxIdx </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> max</span><span class="z-punctuation">(</span><span class="z-source">maxIdx</span><span class="z-punctuation">,</span><span class="z-source"> i </span><span class="z-keyword z-operator">+</span><span class="z-source"> nums</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]);</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">maxIdx </span><span class="z-keyword z-operator">&gt;=</span><span class="z-source"> n </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-true"> true</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-language z-false"> false</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre> <p>注意：如果可达的最大位置超过数组长度，那么将其作为下标访问数组，会出现数组越界的风险吗？</p> <p>不会，在代码中只要可跳跃的最大位置大于等于数组长度-1，就会跳出循环。</p> <hr /> <h2 id="san-zong-jie">三 总结</h2> <p>贪心算法是一种步步为营的策略，每一小步达到最优使得整体达到最优。</p> 2024-11-09T00:00:00+00:00 2024-11-09T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/05-jump-game-ii/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定长度为 <code>n</code> 的整数数组 <code>nums</code> ，每个元素 <code>nums[i]</code> 代表从索引 <code>i</code> 向前跳跃的最大长度。初始位置为 <code>0</code> ，返回达到 <code>n-1</code> 的最小跳跃次数。（假定数组一定能跳到 <code>n-1</code> ）</p> <p><a rel="external" href="https://leetcode.cn/problems/jump-game-ii/">45.跳跃游戏 II</a></p> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-tan-xin-fa">1 贪心法</h3> <h4 id="fen-xi-1-fan-xiang">分析1—反向</h4> <p>直接从前往后找到最优的跳跃位置并计算出其所需花费的跳跃次数，并不是很容易（因为无法从判定当前最优位置的下一个位置仍是否最优）。但已知位置 <code>n-1</code> 必可达，不妨反过来试试从后往前找。</p> <p>假定已经有了第一层的从后往前遍历，那么此时如果第二层循环从前往后遍历，就能找到最优的能跳位置（能从该位置跳跃至当前位置）。因此此时位置越小越优，所以从前往后找到的第一个满足条件的位置即最优位置。</p> <p>之后，只需要每找到一个最优能跳位置，最小步数加1并跳出该层循环。</p> <h4 id="dai-ma-1">代码1</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> jump</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> pos </span><span class="z-keyword z-operator">=</span><span class="z-source"> nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> -</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 当前元素位置</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> minStep </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化最小步数为0</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">pos </span><span class="z-keyword z-operator">&gt;</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 反向遍历数组直到起始位置</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> pos</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 正向遍历找到最优跳跃位置</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">i </span><span class="z-keyword z-operator">+</span><span class="z-source"> nums</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> &gt;=</span><span class="z-source"> pos</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 找到能达到当前位置的位置</span></span> <span class="giallo-l"><span class="z-source"> pos </span><span class="z-keyword z-operator">=</span><span class="z-source"> i</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新当前位置</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">minStep</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 累加步数</span></span> <span class="giallo-l"><span class="z-keyword"> break</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 跳出该层循环</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> minStep</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回最小步数</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fen-xi-2-zheng-xiang">分析2—正向</h4> <p>实际上，计算最小跳跃次数不需要找到最优的跳跃位置，而只要知道最优的可达范围，这可以通过比较现有数组的可达范围而获得。</p> <p>我们的做法是：从位置 <code>0</code> 开始从左往右遍历，记当前可达最大下标位置为一个临界值（作为完成跳跃一次的标志）。当前位置来到临界位置时，跳跃次数加1，直到遍历至最后位置 <code>n-1</code> 。</p> <p>又已知数组经过一定次数跳跃必能达到 <code>n-1</code> 位置，也就是说：在倒数第二次跳跃时，其位置必不在 <code>n-1</code> 位置（可以停下来想一想）。因此只需要遍历数组 <code>[0,n-1)</code> ，而不是 <code>[0,n)</code> 。</p> <h4 id="dai-ma-2">代码2</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> jump</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> nums</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 数组长度</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> minStep </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> maxPos </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> end </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化最小步数，最大下标位置和临界位置为0</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历数组[0,n-1)</span></span> <span class="giallo-l"><span class="z-source"> maxPos </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name z-function"> max</span><span class="z-punctuation">(</span><span class="z-source">maxPos</span><span class="z-punctuation">,</span><span class="z-source"> i </span><span class="z-keyword z-operator">+</span><span class="z-source"> nums</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]);</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新当前最大可达范围</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">i </span><span class="z-keyword z-operator">==</span><span class="z-source"> end</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 判断是否达到临界位置</span></span> <span class="giallo-l"><span class="z-source"> end </span><span class="z-keyword z-operator">=</span><span class="z-source"> maxPos</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新临界值</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">minStep</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 累加最小步数</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> minStep</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回最小步数</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre> <hr /> <h2 id="san-zong-jie">三 总结</h2> <ul> <li> <p>当正向遍历不能解决问题的时候，不妨想想反向遍历。</p> </li> <li> <p>有时候信息不需要明确知道。如：本题中只需知道最小步数的每一步的最优范围，而不需知道每一步的具体位置。</p> </li> </ul> 2024-11-09T00:00:00+00:00 2024-11-09T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/06-merge-sorted-array/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>给定两个非递减顺序的数组 <code>num1</code> 和 <code>nums2</code> ，和另两个表示其有效元素个数的整数 <code>m</code> 和 <code>n</code> 。其中 <code>nums1</code> 实际长度为 <code>m+n</code> ， <code>nums2</code> 实际长度为 <code>n</code> ，请合并 <code>nums2</code> 到 <code>nums1</code> 中去，且合并后的数组 <code>nums1</code> 仍保持非递减顺序。注意： <code>nums1</code> 前 <code>m</code> 个元素表示其有效元素，后 <code>n</code> 个元素为 <code>0</code> 。</p> <p><a rel="external" href="https://leetcode.cn/problems/merge-sorted-array/">88. 合并两个有序数组</a></p> <hr /> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-pai-xu-fa">1 排序法</h3> <h4 id="fen-xi">分析</h4> <p>直接合并两个数组，然后排序。</p> <h4 id="dai-ma">代码</h4> <ul> <li> <p>将数组 <code>nums2</code> 拼接至 <code>nums1</code> 后半部分</p> </li> <li> <p>非递减排序 <code>nums1</code></p> </li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> merge</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums1</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> m</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums2</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> n</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历nums2</span></span> <span class="giallo-l"><span class="z-source"> nums1</span><span class="z-punctuation">[</span><span class="z-source">m </span><span class="z-keyword z-operator">+</span><span class="z-source"> i</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> =</span><span class="z-source"> nums2</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">];</span><span class="z-punctuation z-definition z-comment z-comment"> // 将nums2中元素挪至nums1后半部分</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> sort</span><span class="z-punctuation">(</span><span class="z-source">nums1</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">begin</span><span class="z-punctuation">(),</span><span class="z-source"> nums1</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">end</span><span class="z-punctuation">());</span><span class="z-punctuation z-definition z-comment z-comment"> // 非递减排序nums1</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du">复杂度</h4> <p>时间复杂度为 <code>O((m+n)log(m+n))</code> ，空间复杂度为 <code>O(log(m+n))</code> ，即快速排序长度为 <code>m+n</code> 数组的复杂度。</p> <h3 id="2-shuang-zhi-zhen">2 双指针</h3> <h4 id="fen-xi-1">分析</h4> <p>因为数组 <code>nums1</code> 和 <code>nums2</code> 本是有序数组，因此使用双指针很容易获得二者结合的有序序列：从前往后遍历两数组，取二者元素的较小者，顺序放入结果数组；或从后往前遍历两数组，取二者元素的较大者，逆序放入结果数组。</p> <p>我们本需要额外分配 <code>m+n</code> 的空间来存放结果数组，但 <code>nums1</code> 已在数组末尾分配好额外大小为 <code>n</code> 的空间。此时可发现，使用从后往前的遍历方法，无需考虑覆盖数组 <code>nums1</code> 元素的问题，也无需分配额外空间。</p> <h4 id="dai-ma-1">代码</h4> <ul> <li> <p>初始化两指针 <code>left</code> 和 <code>right</code> 分别指向 <code>nums1</code> 和 <code>nums2</code> 的有效末尾元素，再初始化一指针 <code>cur</code> 指向 <code>nums1</code> 实际末尾元素</p> </li> <li> <p>遍历 <code>nums1</code> 和 <code>nums2</code> 直到完成其中一个</p> </li> <li> <p>拷贝 <code>left</code> 和 <code>right</code> 指向元素的较大者至 <code>cur</code> ，更新指针</p> </li> <li> <p>遍历完后，拷贝 <code>nums2</code> 剩余（如果存在）至 <code>nums1</code></p> </li> <li> <p>注：无需考虑 <code>nums1</code> 存在剩余的情况</p> </li> </ul> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> merge</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums1</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> m</span><span class="z-punctuation">,</span><span class="z-entity z-name z-type"> vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier z-reference z-cpp">&amp;</span><span class="z-variable z-parameter"> nums2</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> n</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> left </span><span class="z-keyword z-operator">=</span><span class="z-source"> m </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">,</span><span class="z-source"> right </span><span class="z-keyword z-operator">=</span><span class="z-source"> n </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 指向nums1、nums2末尾有效元素的指针left、right</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> cur </span><span class="z-keyword z-operator">=</span><span class="z-source"> m </span><span class="z-keyword z-operator">+</span><span class="z-source"> n </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 指向nums1末尾的指针cur</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">left </span><span class="z-keyword z-operator">&gt;=</span><span class="z-constant z-numeric"> 0</span><span class="z-keyword z-operator"> &amp;&amp;</span><span class="z-source"> right </span><span class="z-keyword z-operator">&gt;=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历nums1和nums2直到其中一个完成</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">nums1</span><span class="z-punctuation">[</span><span class="z-source">left</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> &gt;=</span><span class="z-source"> nums2</span><span class="z-punctuation">[</span><span class="z-source">right</span><span class="z-punctuation">]) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 取其中较大者存入位置cur</span></span> <span class="giallo-l"><span class="z-source"> nums1</span><span class="z-punctuation">[</span><span class="z-source">cur</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> =</span><span class="z-source"> nums1</span><span class="z-punctuation">[</span><span class="z-source">left</span><span class="z-punctuation">];</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> --</span><span class="z-source">left</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> nums1</span><span class="z-punctuation">[</span><span class="z-source">cur</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> =</span><span class="z-source"> nums2</span><span class="z-punctuation">[</span><span class="z-source">right</span><span class="z-punctuation">];</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> --</span><span class="z-source">right</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> --</span><span class="z-source">cur</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 更新cur</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">right </span><span class="z-keyword z-operator">&gt;=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 完成nums2剩余遍历（如果需要）</span></span> <span class="giallo-l"><span class="z-source"> nums1</span><span class="z-punctuation">[</span><span class="z-source">cur</span><span class="z-keyword z-operator">--</span><span class="z-punctuation">]</span><span class="z-keyword z-operator"> =</span><span class="z-source"> nums2</span><span class="z-punctuation">[</span><span class="z-source">right</span><span class="z-keyword z-operator">--</span><span class="z-punctuation">];</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // 注：无需考虑num1的剩余遍历</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du-1">复杂度</h4> <ul> <li> <p>最坏情况下，指针移动 <code>m+n</code> 次（ <code>nums1</code> 的最小元素大于 <code>nums2</code> 的最大元素），时间复杂度为 <code>O(m+n)</code></p> </li> <li> <p>数组原地操作，空间复杂度为 <code>O(1)</code></p> </li> </ul> <hr /> <h3 id="san-zong-jie">三 总结</h3> <ul> <li>当需要原地操作数组时，考虑双指针法以有效提升时间和空间复杂度。</li> </ul> <hr /> <p>​</p> 2024-11-09T00:00:00+00:00 2024-11-09T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/07-roman-to-integer/ <h2 id="yi-wen-ti-miao-shu">一 问题描述</h2> <p>罗马数字包含七种字符： <code>I</code> ， <code>V</code> ， <code>X</code> ， <code>L</code> ， <code>C</code> ， <code>D</code> ， <code>M</code> 。</p> <table><thead><tr><th style="text-align: center">字符</th><th style="text-align: center">数值</th></tr></thead><tbody> <tr><td style="text-align: center"><code>I</code></td><td style="text-align: center">1</td></tr> <tr><td style="text-align: center"><code>V</code></td><td style="text-align: center">5</td></tr> <tr><td style="text-align: center"><code>X</code></td><td style="text-align: center">10</td></tr> <tr><td style="text-align: center"><code>L</code></td><td style="text-align: center">50</td></tr> <tr><td style="text-align: center"><code>C</code></td><td style="text-align: center">100</td></tr> <tr><td style="text-align: center"><code>D</code></td><td style="text-align: center">500</td></tr> <tr><td style="text-align: center"><code>M</code></td><td style="text-align: center">1000</td></tr> </tbody></table> <p>例如：罗马数字 <code>2</code> 写做 <code>II</code> ， <code>12</code> 写做 <code>XII</code> ， <code>27</code> 写做 <code>XXVII</code> 。</p> <p>通常情况下罗马数字中小的数字在大的数字右边，但也有特例。如 <code>4</code> 不写做 <code>IIII</code> ，而是 <code>IV</code> ， <code>9</code> 写做 <code>IX</code> 。这个特殊规则如下：</p> <ul> <li> <p><code>I</code> 可以放在 <code>V</code> 和 <code>X</code> 的左边，来表示 <code>4</code> 和 <code>9</code></p> </li> <li> <p><code>X</code> 可以放在 <code>L</code> 和 <code>C</code> 的左边，来表示 <code>40</code> 和 <code>90</code></p> </li> <li> <p><code>C</code> 可以放在 <code>D</code> 和 <code>M</code> 的左边，来表示 <code>400</code> 和 <code>900</code></p> </li> </ul> <p>给定一个表示罗马数字的字符串，将其转换为整数。</p> <p><a rel="external" href="https://leetcode.cn/problems/roman-to-integer/">13. 罗马数字转整数</a></p> <hr /> <h2 id="er-jie-jue-fang-fa">二 解决方法</h2> <h3 id="1-mo-ni">1 模拟</h3> <h4 id="fen-xi">分析</h4> <p>不考虑特殊情况，罗马数字中的七种字符分别代表7个不同数值。也就是说：只要将字符串的每一个字符转换成对应的数值，然后将其累加起来，就可以得到其对应整数。</p> <p>考虑特殊情况，当位于左边的罗马数字小于其右边的时，左边罗马数字取负。</p> <p>使用哈希表存储罗马字符与对应数值的映射关系，便于使用。</p> <h4 id="dai-ma">代码</h4> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Solution</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> romanToInt</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">string</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> unordered_map</span><span class="z-keyword z-operator">&lt;</span><span class="z-storage z-type">char</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> _map </span><span class="z-keyword z-operator">=</span><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-comment z-comment"> // 罗马字符-数值映射表</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-string z-string">&#39;I&#39;</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-string z-string">&#39;V&#39;</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 5</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-string z-string">&#39;X&#39;</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 10</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-string z-string">&#39;L&#39;</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 50</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-string z-string">&#39;C&#39;</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 100</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-string z-string">&#39;D&#39;</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 500</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-string z-string">&#39;M&#39;</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 1000</span><span class="z-punctuation">},</span></span> <span class="giallo-l"><span class="z-punctuation"> };</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> s</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">();</span><span class="z-punctuation z-definition z-comment z-comment"> // 字符串长度</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> sum </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 初始化总和为0（返回值）</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 遍历罗马数字字符串</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> value </span><span class="z-keyword z-operator">=</span><span class="z-source"> _map</span><span class="z-punctuation">[</span><span class="z-source">s</span><span class="z-punctuation">[</span><span class="z-source">i</span><span class="z-punctuation">]];</span><span class="z-punctuation z-definition z-comment z-comment"> // 根据映射表获取当前字符数值</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n </span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric"> 1</span><span class="z-keyword z-operator"> &amp;&amp;</span><span class="z-source"> value </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> _map</span><span class="z-punctuation">[</span><span class="z-source">s</span><span class="z-punctuation">[</span><span class="z-source">i </span><span class="z-keyword z-operator">+</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">]]) {</span><span class="z-punctuation z-definition z-comment z-comment"> // 考虑特殊情况</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">-=</span><span class="z-source"> value</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 当前数值小于右侧数值，取负值</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-keyword"> else</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">+=</span><span class="z-source"> value</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 否则取正值</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-source"> sum</span><span class="z-punctuation">;</span><span class="z-punctuation z-definition z-comment z-comment"> // 返回总和</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">};</span></span></code></pre><h4 id="fu-za-du">复杂度</h4> <ul> <li> <p>只遍历长度为 <code>n</code> 的字符串一次，因此时间复杂度为 <code>O(n)</code> 。</p> </li> <li> <p>只使用常量个变量，因此空间复杂度为 <code>O(1)</code> 。</p> </li> </ul> <hr /> <h2 id="san-zong-jie">三 总结</h2> <ul> <li>有些问题只能根据题意模拟它的解决思路，并没有其他巧妙的方法。</li> </ul> <hr /> 2024-11-09T00:00:00+00:00 2024-11-09T00:00:00+00:00 shaozk https://shaozk.xyz/csdn/08-cpp-primer-chapter-1-exercises/ <h2 id="xi-ti">习题</h2> <h3 id="lian-xi-1-1">练习 1.1</h3> <p>查阅你使用的编译器的文档，确定它所使用的文件命名约定。编译并运行第2页的 <code>main</code> 程序。</p> <pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> man g++</span></span> <span class="giallo-l"><span class="z-support z-function z-builtin">...</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 头文件</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.hh</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.H</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.hp</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.hxx</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.hpp</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.HPP</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.h++</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.tcc</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> C++</span><span class="z-string"> header file to be turned into a precompiled header or Ada spec.</span></span> <span class="giallo-l"></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 源文件</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.cc</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.cp</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.cxx</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.cpp</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.CPP</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.c++</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> file.C</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> C++</span><span class="z-string"> source code that must be preprocessed. Note that in .cxx, the last two letters must both be literally x. Likewise, .C refers to a</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> literal</span><span class="z-string"> capital C.</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-support z-function z-builtin">...</span></span></code></pre><pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_1.cpp</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_1.out demo1_1.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_1.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> echo</span><span class="z-punctuation z-definition z-variable z-source"> $?</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0</span></span></code></pre><h3 id="lian-xi-1-2">练习 1.2</h3> <p>改写程序，让它返回-1。返回值-1通常被当做程序错误的标识。重新编译并运行你的程序，观察你的系统如何处理 <code>main</code> 返回的错误标识符。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_2.cpp</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-keyword z-operator"> -</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_2.out demo1_2.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_2.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> echo</span><span class="z-punctuation z-definition z-variable z-source"> $?</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">255</span></span></code></pre><h3 id="lian-xi-1-3">练习 1.3</h3> <p>编写程序，在标准输出上打印 Hello, World。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_3.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;Hello, Wolrd&quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_3.out demo1_3.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_3.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">Hello,</span><span class="z-string"> Wolrd</span></span></code></pre><h3 id="lian-xi-1-4">练习 1.4</h3> <p>我们的程序使用加法运算符 <code>+</code> 来将两个数相加。编写程序使用乘法运算符来打印两个数的积。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_4.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> v2 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> v2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; * &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> v2 </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; = &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">*</span><span class="z-source"> v2 </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_4.out demo1_4.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_4.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">3</span><span class="z-constant z-numeric"> 4</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">3</span><span class="z-variable"> *</span><span class="z-constant z-numeric"> 4</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 12</span></span></code></pre><h3 id="lian-xi-1-5">练习 1.5</h3> <p>我们将所有的输出操作放在一个很长的语句中。重写程序，将每个运算对象的打印操作放在一条独立的语句中。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_5.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> v2 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> v1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> v2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> v1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; * &quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> v2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; = &quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">*</span><span class="z-source"> v2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_5.out demo1_5.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_5.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">3</span><span class="z-constant z-numeric"> 5</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">3</span><span class="z-variable"> *</span><span class="z-constant z-numeric"> 5</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 15</span></span></code></pre><h3 id="lian-xi-1-6">练习 1.6</h3> <p>解释下面程序片段是否合法。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;The sum of &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> v1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; and &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> v2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; is &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">+</span><span class="z-source"> v2 </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span></code></pre> <p>如果程序是合法的，它输出什么？如果程序不合法，原因何在？应该如何修正？</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_6.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> v2 </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> v2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;The sum of &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> v1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; and &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> v2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; is &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> v1 </span><span class="z-keyword z-operator">+</span><span class="z-source"> v2 </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 不合法，将会报语法错误。因为第一行由&#39;;&#39;结束，说明是一条完整的语句，而第二行输出运算符&#39;&lt;&lt;&#39;左边必须是一个ostream流类型对象，所以会报语法错误。</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 错误信息：</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_6.out demo1_6.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">demo1_6.cpp:</span><span class="z-string"> In function ‘int main</span><span class="z-punctuation">()</span><span class="z-string">’:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">demo1_6.cpp:9:9:</span><span class="z-string"> error: expected primary-expression before ‘</span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string">’</span><span class="z-entity z-name z-function"> token</span></span> <span class="giallo-l"><span class="z-string"> 9 | &lt;&lt; &quot; and &quot; &lt;&lt; v2;</span></span> <span class="giallo-l"><span class="z-string"> | ^~</span></span> <span class="giallo-l"><span class="z-string">demo1_6.cpp:10:9: error: expected primary-expression before ‘&lt;&lt;’ token</span></span> <span class="giallo-l"><span class="z-string"> 10 | &lt;&lt; &quot; is &quot; &lt;&lt; v1 + v2 &lt;&lt; std::endl;</span></span> <span class="giallo-l"><span class="z-string"> | ^~</span></span> <span class="giallo-l"><span class="z-string"> </span></span> <span class="giallo-l"><span class="z-string"># 将每行代码末尾分号&#39;;&#39;移除即可修正，具体代码如下：</span></span> <span class="giallo-l"><span class="z-string">std::cout &lt;&lt; &quot;The sum of &quot; &lt;&lt; v1</span></span> <span class="giallo-l"><span class="z-string"> &lt;&lt; &quot; and &quot; &lt;&lt; v2</span></span> <span class="giallo-l"><span class="z-string"> &lt;&lt; &quot; is &quot; &lt;&lt; v1 + v2 &lt;&lt; std::endl;</span></span></code></pre><h3 id="lian-xi-1-7">练习 1.7</h3> <p>编译一个包含不正确的嵌套注释的程序，观察编译器返回的错误信息。</p> <pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_7.out demo1_7.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">demo1_7.cpp:</span><span class="z-string"> In function ‘int main</span><span class="z-punctuation">()</span><span class="z-string">’:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">demo1_7.cpp:5:11:</span><span class="z-string"> error: expected primary-expression before ‘/’ token</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> 5</span><span class="z-keyword z-operator"> |</span><span class="z-entity z-name z-function"> /*</span><span class="z-variable"> *</span><span class="z-string">/</span><span class="z-variable">*</span><span class="z-string">/</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> |</span><span class="z-entity z-name z-function"> ^</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">demo1_7.cpp:6:5:</span><span class="z-string"> error: expected primary-expression before ‘return’</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> 6</span><span class="z-keyword z-operator"> |</span><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> |</span><span class="z-entity z-name z-function"> ^~~~~~</span></span></code></pre><h3 id="lian-xi-1-8">练习 1.8</h3> <p>指出下列哪些输出语句是合法的（如果有的话）：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;/*&quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;*/&quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-comment z-comment"> /* &quot;*/</span><span class="z-punctuation z-definition z-string z-string">&quot; */;</span></span> <span class="giallo-l"><span class="z-string z-punctuation z-definition z-string">std::cout &lt;&lt; /* &quot;</span><span class="z-source">*/</span><span class="z-punctuation z-definition z-string z-string">&quot; /* &quot;</span><span class="z-punctuation z-definition z-comment z-comment">/*&quot; */</span><span class="z-punctuation">;</span></span></code></pre> <p>预测编译这些语句会产生什么样的结果，实际编译这些语句来验证你的答案（编写一个小程序，每次将上述一条语句作为其主体），改正每个编译错误。</p> <pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">1</span><span class="z-string"> 正确</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">2</span><span class="z-string"> 正确</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">3</span><span class="z-string"> 错误 双引号缺少结束符</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">4</span><span class="z-string"> 正确</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">//</span><span class="z-string"> demo1_8_1.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">#include &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name z-function">int</span><span class="z-string"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> std::cout</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot;/*&quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-string"> return 0;</span></span> <span class="giallo-l"><span class="z-string">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_8_1.out demo1_8_1.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_8_1.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">/*$</span><span class="z-source"> </span></span></code></pre><pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_8_2.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;*/&quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">/*g++</span><span class="z-string"> -o demo1_8_2.out demo1_8_2.cpput</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_8_2.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword z-operator">*</span><span class="z-source">/$ </span></span></code></pre><pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_8_3.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-comment z-comment"> /* &quot;*/</span><span class="z-punctuation z-definition z-string z-string">&quot; */;</span></span> <span class="giallo-l"><span class="z-string"> return 0;</span></span> <span class="giallo-l"><span class="z-string">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-keyword z-operator">*</span><span class="z-source">/g++ -o demo1_8_3.out demo1_8_3.cpput </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">demo1_8_3.cpp:6:24:</span><span class="z-string z-punctuation z-definition z-string"> warning: missing terminating &quot; character</span></span> <span class="giallo-l"><span class="z-string z-punctuation z-definition z-string"> 6 | std::cout &lt;&lt; /* &quot;</span><span class="z-variable">*</span><span class="z-string z-punctuation z-definition z-string">/&quot; */;</span></span> <span class="giallo-l"><span class="z-string"> | ^</span></span> <span class="giallo-l"><span class="z-string z-punctuation z-definition z-string">demo1_8_3.cpp:6:24: error: missing terminating &quot; character</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> 6</span><span class="z-keyword z-operator"> |</span><span class="z-entity z-name z-function"> std::cout</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string"> /*</span><span class="z-entity z-name z-function"> &quot;*/&quot;</span><span class="z-variable"> *</span><span class="z-string">/</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-string"> | ^~~~~</span></span> <span class="giallo-l"><span class="z-string">demo1_8_3.cpp: In function ‘int main()’:</span></span> <span class="giallo-l"><span class="z-string">demo1_8_3.cpp:7:5: error: expected primary-expression before ‘return’</span></span> <span class="giallo-l"><span class="z-string"> 7 | return 0;</span></span> <span class="giallo-l"><span class="z-string"> | ^~~~~~</span></span></code></pre><pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-source">$ g</span><span class="z-keyword z-operator">++ -</span><span class="z-source">o demo1_8_4</span><span class="z-punctuation">.</span><span class="z-source">out demo1_8_4</span><span class="z-punctuation">.</span><span class="z-source">cpp </span></span> <span class="giallo-l"><span class="z-source">$ .</span><span class="z-keyword z-operator">/</span><span class="z-source">demo1_8_4</span><span class="z-punctuation">.</span><span class="z-source">out </span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> /* $ </span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_8_4.out demo1_8_4.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_8_4.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> /*</span><span class="z-source"> $ </span></span></code></pre><h3 id="lian-xi-1-9">练习 1.9</h3> <p>编写程序，使用 <code>while</code> 循环将50到100的整数相加。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_9.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> a </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 50</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> sum </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source"> a </span><span class="z-keyword z-operator">&lt;=</span><span class="z-constant z-numeric"> 100</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">+=</span><span class="z-source"> a</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> a</span><span class="z-keyword z-operator">++</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;sum = &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> sum </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> /g++ -o demo1_9.out demo1_9.cpp.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_9.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sum</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 3825</span></span></code></pre><h3 id="lian-xi-1-10">练习 1.10</h3> <p>除了 <code>++</code> 运算符将运算对象的值增加1之外，还有一个递减运算符（ <code>--</code> ）实现将值减少1。编写程序，使用递减运算符在循环中按递减顺序打印出10到0之间的整数。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_10.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> a </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 10</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source"> a </span><span class="z-keyword z-operator">&gt;=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> a </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> a</span><span class="z-keyword z-operator">--</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_10.out demo1_10.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_10.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">10</span><span class="z-constant z-numeric"> 9 8 7 6 5 4 3 2 1 0</span><span class="z-source"> </span></span></code></pre><h3 id="lian-xi-1-11">练习 1.11</h3> <p>编写程序，提示用户输入两个整数，打印这两个整数所有指定的范围内的所有整数。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_11.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> a </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> b </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> cur </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;Input two number:</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation z-definition z-string">&quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> a </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> b</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">a </span><span class="z-keyword z-operator">&lt;=</span><span class="z-source"> b</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> cur </span><span class="z-keyword z-operator">=</span><span class="z-source"> a</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">cur </span><span class="z-keyword z-operator">&lt;=</span><span class="z-source"> b</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> cur </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> cur</span><span class="z-keyword z-operator">++</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> else</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> cur </span><span class="z-keyword z-operator">=</span><span class="z-source"> a</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">cur </span><span class="z-keyword z-operator">&gt;=</span><span class="z-source"> b</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> cur </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-source"> cur</span><span class="z-keyword z-operator">--</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_11.out demo1_11.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_11.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">Input</span><span class="z-string"> two number:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">2</span><span class="z-constant z-numeric"> 5</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">2</span><span class="z-constant z-numeric"> 3 4 5</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_11.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">Input</span><span class="z-string"> two number:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">5</span><span class="z-constant z-numeric"> 2</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">5</span><span class="z-constant z-numeric"> 4 3 2</span><span class="z-source"> </span></span></code></pre><h3 id="lian-xi-1-12">练习 1.12</h3> <p>下面的 <code>for</code> 循环完成了什么功能？sum的终值是多少？</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-source"> sum </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword">for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;=</span><span class="z-constant z-numeric"> 100</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">+=</span><span class="z-source"> i</span><span class="z-punctuation">;</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 计算从0到100之间整数的总和</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 5050</span></span></code></pre><pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_12.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> sum </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;=</span><span class="z-constant z-numeric"> 100</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">+=</span><span class="z-source"> i</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;sum = &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> sum </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ -o demo1_12.out demo1_12.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./demo1_12.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sum</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 5050</span></span></code></pre><h3 id="lian-xi-1-13">练习 1.13</h3> <p>使用 <code>for</code> 循环重做1.4.1节中的所有练习（第11页）。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_13_1.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> sum </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> num </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 50</span><span class="z-punctuation">;</span><span class="z-source"> num </span><span class="z-keyword z-operator">&lt;=</span><span class="z-constant z-numeric"> 100</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">num</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">+=</span><span class="z-source"> num</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;sum = &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> sum </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_13_2.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 10</span><span class="z-punctuation">;</span><span class="z-source"> n </span><span class="z-keyword z-operator">&gt;</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> --</span><span class="z-source">n</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;n = &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> n </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span> <span class="giallo-l"></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_13_3.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-storage z-type">using namespace</span><span class="z-entity z-name z-namespace"> std</span><span class="z-punctuation">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> m</span><span class="z-punctuation">,</span><span class="z-source"> n</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;Please input 2 number:&quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> m </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">m </span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> n</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> tmp </span><span class="z-keyword z-operator">=</span><span class="z-source"> m</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> m </span><span class="z-keyword z-operator">=</span><span class="z-source"> n</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> n </span><span class="z-keyword z-operator">=</span><span class="z-source"> tmp</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-source"> m</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">) {</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># demo1_13_1.cpp</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_13_1.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sum</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 3825</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># demo1_13_2.cpp</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_13_2.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 10</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 9</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 8</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 7</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 6</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 5</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 4</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 3</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 2</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">n</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 1</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># demo1_13_3.cpp</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_13_3.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">Please</span><span class="z-string"> input</span><span class="z-constant z-numeric"> 2</span><span class="z-string"> number:10</span><span class="z-constant z-numeric"> 1</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">1</span><span class="z-constant z-numeric"> 2 3 4 5 6 7 8 9</span><span class="z-source"> </span></span> <span class="giallo-l"></span></code></pre><h3 id="lian-xi-1-14">练习 1.14</h3> <p>对比 <code>for</code> 循环和 <code>while</code> 循环，两种形式的优缺点各是什么？</p> <pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 对于for循环，有三个控制条件：初始值、结束值和步进值，其形式更为集中、简洁，且适用于循环次数已知的情况。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 对于while循环，使用特定条件控制循环是否执行，适用于循环次数未知的情况。</span></span></code></pre><h3 id="lian-xi-1-15">练习 1.15</h3> <p>编写程序，包含第14页“再探编译”中讨论的常见错误。熟悉编译器生成的错误信息。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_15.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // 错误：endl后使用了冒号而非分号</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;Read each file.&quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // 错误：字符串字面值常量的两侧漏掉了引号</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> Update master. </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // 错误：漏掉了第二个输出运算符</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;Write new master.&quot;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"> // 错误：return语句漏掉了分号</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 其中只有最后一个错误精准找到了 </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_15.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">demo1_15.cpp:</span><span class="z-string"> In function ‘int main</span><span class="z-punctuation">()</span><span class="z-string">’:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">demo1_15.cpp:6:48:</span><span class="z-string"> error: found ‘:’ in nested-name-specifier, expected ‘::’</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> 6</span><span class="z-keyword z-operator"> |</span><span class="z-entity z-name z-function"> std::cout</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot;Read each file.&quot;</span><span class="z-source"> &lt;&lt;</span><span class="z-entity z-name z-function"> std::endl:</span></span> <span class="giallo-l"><span class="z-string"> | ^</span></span> <span class="giallo-l"><span class="z-string"> | ::</span></span> <span class="giallo-l"><span class="z-string">demo1_15.cpp:6:44: error: ‘std::endl’ is not a class, namespace, or enumeration</span></span> <span class="giallo-l"><span class="z-string"> 6 | std::cout &lt;&lt; &quot;Read each file.&quot; &lt;&lt; std::endl:</span></span> <span class="giallo-l"><span class="z-string"> | ^~~~</span></span> <span class="giallo-l"><span class="z-string">demo1_15.cpp:7:18: error: ‘Update’ was not declared in this scope</span></span> <span class="giallo-l"><span class="z-string"> 7 | std::cout &lt;&lt; Update master. &lt;&lt; std::endl;</span></span> <span class="giallo-l"><span class="z-string"> | ^~~~~~</span></span> <span class="giallo-l"><span class="z-string">demo1_15.cpp:8:37: error: expected ‘;’ before ‘std’</span></span> <span class="giallo-l"><span class="z-string"> 8 | std::cout &lt;&lt; &quot;Write new master.&quot; std::endl;</span></span> <span class="giallo-l"><span class="z-string"> | ^~~~</span></span> <span class="giallo-l"><span class="z-string"> | ;</span></span> <span class="giallo-l"><span class="z-string">demo1_15.cpp:9:13: error: expected ‘;’ before ‘}’ token</span></span> <span class="giallo-l"><span class="z-string"> 9 | return 0</span></span> <span class="giallo-l"><span class="z-string"> | ^</span></span> <span class="giallo-l"><span class="z-string"> | ;</span></span> <span class="giallo-l"><span class="z-string"> 10 | }</span></span> <span class="giallo-l"><span class="z-string"> | ~ </span></span> <span class="giallo-l"></span></code></pre><h3 id="lian-xi-1-16">练习 1.16</h3> <p>编写程序，从 <code>cin</code> 读取一组数，输出其和。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_16.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> sum </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> value </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> value</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">+=</span><span class="z-source"> value</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;sum = &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> sum </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_16.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">3</span><span class="z-constant z-numeric"> 4</span><span class="z-string"> 5^E</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">sum</span><span class="z-string"> =</span><span class="z-constant z-numeric"> 12</span></span></code></pre><h3 id="lian-xi-1-17">练习 1.17</h3> <p>如果输入的所有值是相等的，本节的程序会输出什么？如果没有重复值，输出又会是什么？</p> <pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 当输入的所有值是相等时，程序会计算该值出现的次数。</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 没有重复值时，每个值计数一次</span></span></code></pre><h3 id="lian-xi-1-18">练习 1.18</h3> <p>编译并运行本节的程序，给它输入全都相等的值。再次运行程序，输入没有重复的值。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_17.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> currVal </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">,</span><span class="z-source"> val </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> currVal</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> cnt </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> val</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">val </span><span class="z-keyword z-operator">==</span><span class="z-source"> currVal</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">cnt</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> else</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> currVal </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; occurs &quot;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> cnt </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; times&quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> currVal </span><span class="z-keyword z-operator">=</span><span class="z-source"> val</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> cnt </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> currVal </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; occurs &quot;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> cnt </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot; times&quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_18.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">1</span><span class="z-constant z-numeric"> 1 1 1 1 1 1</span><span class="z-string"> 1^E</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">1</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 8</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">1</span><span class="z-constant z-numeric"> 2 3 4 5 6 7 8</span><span class="z-string"> 9^E</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">1</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">2</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">3</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">4</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">5</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">6</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">7</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">8</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">9</span><span class="z-string"> occurs</span><span class="z-constant z-numeric"> 1</span><span class="z-string"> times</span></span></code></pre><h3 id="lian-xi-1-19">练习 1.19</h3> <p>修改你为1.4.1节练习1.10（第11页）所编写的程序（打印一个范围内的数），使其能处理用户输入的第一个数比第二个数小的情况。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_19.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-storage z-type">using namespace</span><span class="z-entity z-name z-namespace"> std</span><span class="z-punctuation">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> m</span><span class="z-punctuation">,</span><span class="z-source"> n</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;Please input 2 number:&quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> m </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">m </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-source"> m</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> ++</span><span class="z-source">i</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> else</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">int</span><span class="z-source"> i </span><span class="z-keyword z-operator">=</span><span class="z-source"> m</span><span class="z-punctuation">;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> n</span><span class="z-punctuation">;</span><span class="z-keyword z-operator"> --</span><span class="z-source">i</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> i </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_19.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">Please</span><span class="z-string"> input</span><span class="z-constant z-numeric"> 2</span><span class="z-string"> number:1</span><span class="z-constant z-numeric"> 10</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">1</span><span class="z-constant z-numeric"> 2 3 4 5 6 7 8 9</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">Please</span><span class="z-string"> input</span><span class="z-constant z-numeric"> 2</span><span class="z-string"> number:10</span><span class="z-constant z-numeric"> 1</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">10</span><span class="z-constant z-numeric"> 9 8 7 6 5 4 3 2</span><span class="z-source"> </span></span></code></pre><h3 id="lian-xi-1-20">练习 1.20</h3> <p>在网站http://www.informit.com/title/03217714113 上，第1章的代码目录包含了头文件 <code>Sales_item.h</code> 。将它拷贝到你自己的工作目录。用它编写一个程序，读取一组书籍销售记录，将每条记录打印到标准输出上。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_20.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &quot;include/Sales_item.h&quot;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-storage z-type">using namespace</span><span class="z-entity z-name z-namespace"> std</span><span class="z-punctuation">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> Sales_item item</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> item</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> item </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_20.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 3 20.00</span><span class="z-string"> 0-201-78346-X</span><span class="z-constant z-numeric"> 4 40.00</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 3 60 20</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78346-X</span><span class="z-constant z-numeric"> 4 160 40</span></span></code></pre><h3 id="lian-xi-1-21">练习 1.21</h3> <p>编写程序，读取两个ISBN相同的 <code>Sales_Item</code> 对象，输出它们的和。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_21.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &quot;include/Sales_item.h&quot;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-storage z-type">using namespace</span><span class="z-entity z-name z-namespace"> std</span><span class="z-punctuation">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> Sales_item item1</span><span class="z-punctuation">,</span><span class="z-source"> item2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> item1 </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> item2</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">item1</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> ==</span><span class="z-source"> item2</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">())</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> item1 </span><span class="z-keyword z-operator">+</span><span class="z-source"> item2</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_21.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 3 20.00</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 5 20.00</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 8 160 20</span><span class="z-source">$ </span></span></code></pre><h3 id="lian-xi-1-22">练习 1.22</h3> <p>编写程序，读取多个具有相同ISBN的销售记录，输出所有记录的和。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_22.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &quot;include/Sales_item.h&quot;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-storage z-type">using namespace</span><span class="z-entity z-name z-namespace"> std</span><span class="z-punctuation">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> Sales_item item</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> Sales_item sum</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> item</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">=</span><span class="z-source"> item</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> item</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">item</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> ==</span><span class="z-source"> sum</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">())</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> sum </span><span class="z-keyword z-operator">+=</span><span class="z-source"> item</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> sum </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 3 20.00</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 4 20.00</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 5</span><span class="z-string"> 20.00^E</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">^E</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 12 240 20</span></span></code></pre><h3 id="lian-xi-1-23">练习 1.23</h3> <p>编写程序，读取多条销售记录，并统计一个ISBN（每本书）有几条销售记录。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_23.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &quot;include/Sales_item.h&quot;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-storage z-type">using namespace</span><span class="z-entity z-name z-namespace"> std</span><span class="z-punctuation">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> Sales_item start</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> start</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> cnt </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> Sales_item item</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> item</span><span class="z-punctuation">)</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">item</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> ==</span><span class="z-source"> start</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">())</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> ++</span><span class="z-source">cnt</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> else</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> start</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> cnt </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> cnt </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> start </span><span class="z-keyword z-operator">=</span><span class="z-source"> item</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-source"> cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> start</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-punctuation z-definition z-string"> &quot; &quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> cnt </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_23.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 4 20.00</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 6 30.00</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78346-X</span><span class="z-constant z-numeric"> 7</span><span class="z-string"> 30.00^E</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 2</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">^E</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78346-X</span><span class="z-constant z-numeric"> 1</span></span></code></pre><h3 id="lian-xi-1-24">练习 1.24</h3> <p>输入表示多个ISBN的多条销售记录来测试上一个程序，每个ISBN的记录应该聚在一起。</p> <pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment"># 见习题1.23</span></span></code></pre><h3 id="lian-xi-1-25">练习 1.25</h3> <p>借助网站上的 <code>Sales_Item.h</code> 头文件，编译并运行本节给出的书店程序。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-punctuation z-definition z-comment z-comment">// demo1_25.cpp</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &lt;iostream&gt;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-directive z-keyword z-control z-directive">#include</span><span class="z-punctuation z-definition z-string z-string"> &quot;include/Sales_item.h&quot;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">int</span><span class="z-entity z-name z-function"> main</span><span class="z-punctuation">()</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> Sales_item total</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> total</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> Sales_item trans</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> while</span><span class="z-punctuation"> (</span><span class="z-entity z-name z-scope-resolution z-cpp">std</span><span class="z-punctuation">::</span><span class="z-source">cin </span><span class="z-keyword z-operator">&gt;&gt;</span><span class="z-source"> trans</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> if</span><span class="z-punctuation"> (</span><span class="z-source">total</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">()</span><span class="z-keyword z-operator"> ==</span><span class="z-source"> trans</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">isbn</span><span class="z-punctuation">())</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> total </span><span class="z-keyword z-operator">+=</span><span class="z-source"> trans</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> else</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> total </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-source"> total </span><span class="z-keyword z-operator">=</span><span class="z-source"> trans</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-source"> total </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-keyword"> else</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">cerr </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation z-definition z-string z-string"> &quot;No data?&quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-entity z-name z-scope-resolution z-cpp"> std</span><span class="z-punctuation">::</span><span class="z-source">endl</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-keyword z-operator"> -</span><span class="z-constant z-numeric">1</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword"> return</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre><pre class="giallo z-code"><code data-lang="shellscript"><span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> g++ demo1_25.cpp</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">$</span><span class="z-string"> ./a.out</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 3 20.0</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 2 25.0</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78346-X</span><span class="z-constant z-numeric"> 4 40.0</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78345-X</span><span class="z-constant z-numeric"> 5 110 22</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78347-X</span><span class="z-constant z-numeric"> 7 70.0</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78346-X</span><span class="z-constant z-numeric"> 4 160 40</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">^E</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">^E</span></span> <span class="giallo-l"><span class="z-entity z-name z-function">0-201-78347-X</span><span class="z-constant z-numeric"> 7 490 70</span></span></code></pre><h2 id="zong-jie">总结</h2> <p>第一章总体来说十分简单，主要介绍有：</p> <ul> <li> <p>C++程序的编译与运行</p> </li> <li> <p>输入与输出（ <code>std::cin</code> 和 <code>std::cout</code> ）</p> </li> <li> <p>注释（ <code>//</code> 和 <code>/* */</code> ）</p> </li> <li> <p>控制语句，包括 <code>while</code> 循环、 <code>for</code> 循环和 <code>if</code> 语句</p> </li> <li> <p>类简单使用，包括对象声明、类的成员函数调用以及类的 <code>+ - * / =</code> 操作（前提是需要在类定义时重载这些运算符）</p> </li> </ul>