一道小算法题-随机取出一首诗-算法剖析

本文介绍了如何使用算法从唐诗三百首文本文件中随机选取一首诗,通过PHP的file_get_contents函数读取文本,然后进行处理。详细解析了实现这一功能的代码步骤。
<span style="font-size:24px;">上周,主管出了一道题,从唐诗三百首(如下图,一个txt文档)里随机输出一首诗</span>
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<img src="https://img-blog.youkuaiyun.com/20150417175303652?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvY3NsMDA4/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />

<span style="font-size:24px;">下面把算法上了逐个分析</span>
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<span style="font-size:24px;">算法1:</span>
<div class="line number1 index0 alt2" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; white-space: pre-wrap !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$ts300</code> <code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">= </code><code class="php functions" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(255, 20, 147) !important; background: none !important;">file_get_contents</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">(</code><code class="php string" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 51, 102) !important; background: none !important;">"300.txt"</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">);</code></div><div class="line number2 index1 alt1" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; white-space: pre-wrap !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">preg_match_all(</code><code class="php string" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 51, 102) !important; background: none !important;">'/\d\d\d(.*?)(?=\d)/ms'</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">, </code><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$ts300</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">, </code><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$match</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">);</code></div><div class="line number3 index2 alt2" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; white-space: pre-wrap !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$shi</code> <code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">= </code><code class="php functions" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(255, 20, 147) !important; background: none !important;">array_rand</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">(</code><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$match</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">[1]);</code></div><div class="line number4 index3 alt1" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; white-space: pre-wrap !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"> </div><div class="line number5 index4 alt2" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; white-space: pre-wrap !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php functions" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(255, 20, 147) !important; background: none !important;">echo</code> <code class="php string" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 51, 102) !important; background: none !important;">"<pre>"</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">;</code></div><div class="line number6 index5 alt1" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; white-space: pre-wrap !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php functions" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(255, 20, 147) !important; background: none !important;">echo</code> <code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$match</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">[1][</code><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$shi</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">];</code></div><div class="line number7 index6 alt2" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; white-space: pre-wrap !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php functions" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(255, 20, 147) !important; background: none !important;">echo</code> <code class="php string" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 51, 102) !important; background: none !important;">"</pre>"</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">;</code></div><div class="line number7 index6 alt2" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; white-space: pre-wrap !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;">
</div><span style="font-size:24px;">file_get_contents 复杂度为O(n),</span>
<span style="font-size:24px;">preg_match_all 复杂度为O(n),</span>
<span style="font-size:24px;">array_rand复杂度会单独开篇讲,</span>
<span style="font-size:24px;">所以算法1的复杂度 为O(2n)</span>
=========================================================================================================================================
<span style="font-size:24px;">算法2:</span>
<div class="line number6 index5 alt1" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: pre-wrap; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em 0px 0em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$file_handle</code> <code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">= </code><code class="php functions" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(255, 20, 147) !important; background: none !important;">fopen</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">(</code><code class="php string" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 51, 102) !important; background: none !important;">"300.txt"</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">, </code><code class="php string" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 51, 102) !important; background: none !important;">"r"</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">);</code></div><div class="line number7 index6 alt2" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: pre-wrap; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em 0px 0em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$i</code> <code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">= 1;</code></div><div class="line number8 index7 alt1" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: pre-wrap; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em 0px 0em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php keyword" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-weight: bold !important; font-size: 14px !important; min-height: inherit !important; color: rgb(51, 102, 153) !important; background: none !important;">while</code> <code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">(!</code><code class="php functions" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(255, 20, 147) !important; background: none !important;">feof</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">(</code><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$file_handle</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">))</code></div><div class="line number9 index8 alt2" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: pre-wrap; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em 0px 0em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">{</code></div><div class="line number10 index9 alt1" style="line-height: 20px; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace; font-size: 15px; white-space: pre-wrap; color: rgb(51, 51, 51); border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px 1em 0px 0em !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; min-height: inherit !important; background-image: none !important; background-attachment: initial !important; background-size: initial !important; background-origin: initial !important; background-clip: initial !important; background-position: initial !important; background-repeat: initial !important;"><code class="php spaces" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; background: none !important;">    </code><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$line</code> <code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">= </code><code class="php functions" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(255, 20, 147) !important; background: none !important;">fgets</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(0, 0, 0) !important; background: none !important;">(</code><code class="php variable" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; margin: 0px !important; outline: 0px !important; overflow: visible !important; padding: 0px !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-size: 14px !important; min-height: inherit !important; color: rgb(170, 119, 0) !important; background: none !important;">$file_handle</code><code class="php plain" style="font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !
<think>嗯,用户让我介绍一下算法2-3,也就是从顺序表中删除第i个元素。首先,我需要确认自己对顺序表的基本结构是否清楚。顺序表通常是用数组实现的线性表,元素在内存中连续存储。那删除操作的话,应该涉及到移动元素来填补被删除的位置,以保证连续性。 首先,我得回忆删除第i个元素的步骤。可能第一步要检查i的合法性,比如i是否在有效范围内。比如,如果顺序表长度是n,那么i的范围应该是1 ≤ i ≤ n,或者可能从0开始索引,需要确定这一点。用户提到的是算法2-3,可能教材中的索引是从1开始的,所以需要注意这点。 接下来,假设i是合法的,那么要删除第i个元素,需要将后面的元素都往前移动一位。比如,假设数组索引从0开始,第i个元素对应的位置是i-1。删除之后,从i的位置开始,后面的元素都要前移,覆盖掉被删除的元素,这样后面的元素就依次填补空缺,同时长度减1。 这时候需要考虑时间复杂度。因为需要移动元素,平均和最坏情况下的时间复杂度都是O(n),因为可能需要移动n-i个元素。而如果i是最后一个元素,则不需要移动,时间复杂度O(1)。 然后,用户可能需要具体的步骤描述,比如伪代码或者算法流程。例如: 1. 检查i的有效性,如果i不在1到n之间,则报错或返回异常。 2. 取出被删除的元素的值(如果需要的话)。 3. 从第i+1个元素到最后一个元素,依次前移一个位置。 4. 表长减1。 不过,用户可能更关心具体的实现细节,比如在代码中如何处理元素的移动。例如,在C语言中,可能用循环来覆盖元素: for (int j = i; j < n; j++) { list[j-1] = list[j]; } 这时候要注意数组越界的问题,以及索引是否正确。 另外,还要考虑顺序表的其他属性,比如当前长度变量是否需要更新。比如,顺序表结构体可能包含一个数组和一个length字段,删除后需要将length减1。 可能用户还容易混淆顺序表和链表的删除操作区别。顺序表需要移动元素,而链表只需要修改指针,所以时间复杂度不同。这点可能需要强调。 用户的问题可能是在学习数据结构,所以需要详细解释每一步的原因,比如为什么要移动元素,为什么检查i的范围很重要。例如,如果i无效,可能导致数组访问越界,引发错误。 另外,可能还需要举一个例子,比如删除第3个元素,在顺序表中的变化过程。比如原表是[10,20,30,40,50],删除第三个元素30后,后面的40和50前移,变成[10,20,40,50],长度减为4。 还要注意,删除操作是否返回被删除的元素,这取决于具体实现,但算法的主要步骤是移动元素和调整长度。 总结下来,回答的结构应该是先介绍顺序表的结构,然后详细说明删除步骤,包括参数检查、元素移动、长度调整,时间复杂度分析,可能还要举例说明,以及注意事项,比如索引范围等。这样用户能够逐步理解整个过程。</think>好的,我将按照数据结构标准流程为您解释顺序表删除第i个元素的算法实现: ### 算法思想 顺序表(数组实现)的删除操作需要保持元素连续性。删除第i个元素后,需将后续所有元素向前移动一个位置,时间复杂度为$O(n)$。 ### 具体步骤 1. **参数校验** 验证$i$的有效性:满足$1 \leq i \leq n$(假设元素序号从1开始计数) 2. **元素移动** 从第$i+1$个元素到最后一个元素,依次前移一位: $$\text{for } j = i \text{ to } n-1: \quad list[j-1] \leftarrow list[j]$$ 3. **更新表长** 将当前表长$n$减1 ### 伪代码实现 ```text 算法2-3 DeleteElem(List, i) 输入:顺序表List,删除位置i 输出:更新后的顺序表 1. if i < 1 OR i > List.length ▷ 有效性检查 2. throw "非法位置" 3. deleted_element ← List.data[i-1] ▷ 保存被删元素(可选) 4. for j ← i TO List.length-1 ▷ 注意数组下标从0开始 5. List.data[j-1] ← List.data[j] 6. List.length ← List.length - 1 7. return List ``` ### 示例演示 假设顺序表存储`[5,3,9,2,7]`,删除第3个元素(值=9): ``` 删除前索引:0 1 2 3 4 [5,3,9,2,7] 删除操作后: [5,3,2,7,7] → 实际有效数据 [5,3,2,7] → 表长减1后 ``` ### 注意事项 1. **时间复杂度**:最好情况$O(1)$(删除末尾元素),最坏$O(n)$(删除首元素) 2. **空间复杂度**:$O(1)$(无需额外存储空间) 3. **索引约定**:不同教材可能使用0-based或1-based索引,需特别注意算法实现中的下标转换 4. **稳定性**:删除操作会改变元素原始位置,属于不稳定操作 ### 扩展思考 与链表删除操作对比: - 顺序表:适合随机访问,但删除效率与位置相关 - 链表:删除时间复杂度恒为$O(1)$(已定位节点),但需要额外存储指针 这个算法是理解线性表操作的基础,后续在实现栈、队列等数据结构时会频繁使用类似操作逻辑。
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