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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>计算两个字符串之间的编辑距离</title>
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</head>
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<body class="docs"><div id="layout">
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<div id="layout-content"><div id="function.levenshtein" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">levenshtein</h1>
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<p class="verinfo">(PHP 4 >= 4.0.1, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">levenshtein</span> — <span class="dc-title">计算两个字符串之间的编辑距离</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.levenshtein-description">
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<h3 class="title">说明</h3>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>levenshtein</strong></span>
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( <span class="methodparam"><span class="type">string</span> <code class="parameter">$str1</code></span>
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, <span class="methodparam"><span class="type">string</span> <code class="parameter">$str2</code></span>
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) : <span class="type">int</span></div>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>levenshtein</strong></span>
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( <span class="methodparam"><span class="type">string</span> <code class="parameter">$str1</code></span>
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, <span class="methodparam"><span class="type">string</span> <code class="parameter">$str2</code></span>
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, <span class="methodparam"><span class="type">int</span> <code class="parameter">$cost_ins</code></span>
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, <span class="methodparam"><span class="type">int</span> <code class="parameter">$cost_rep</code></span>
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, <span class="methodparam"><span class="type">int</span> <code class="parameter">$cost_del</code></span>
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) : <span class="type">int</span></div>
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<p class="para rdfs-comment">
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编辑距离，是指两个字串之间，通过替换、插入、删除等操作将字符串<code class="parameter">str1</code>转换成<code class="parameter">str2</code>所需要操作的最少字符数量。
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该算法的复杂度是 <em>O(m*n)</em>，其中 <em>n</em> 和 <em>m</em> 分别是<code class="parameter">str1</code> 和<code class="parameter">str2</code>的长度 （当和算法复杂度为O(max(n,m)**3)的<span class="function"><a href="similar_text.html" class="function">similar_text()</a></span>相比时，此函数还是相当不错的，尽管仍然很耗时。）。
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</p>
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<p class="para">
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在最简单的形式中，该函数只以两个字符串作为参数，并计算通过插入、替换和删除等操作将<code class="parameter">str1</code>转换成<code class="parameter">str2</code>所需要的操作次数。
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</p>
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<p class="para">
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第二种变体将采用三个额外的参数来定义插入、替换和删除操作的次数。此变体比第一种更加通用和适应，但效率不高。
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.levenshtein-parameters">
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<h3 class="title">参数</h3>
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<p class="para">
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<dl>
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<dt>
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<code class="parameter">str1</code></dt>
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<dd>
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<p class="para">
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求编辑距离中的其中一个字符串
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</p>
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</dd>
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<dt>
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<code class="parameter">str2</code></dt>
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<dd>
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<p class="para">
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求编辑距离中的另一个字符串
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</p>
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</dd>
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<dt>
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<code class="parameter">cost_ins</code></dt>
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<dd>
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<p class="para">
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定义插入次数
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</p>
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</dd>
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<dt>
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<code class="parameter">cost_rep</code></dt>
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<dd>
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<p class="para">
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定义替换次数
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</p>
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</dd>
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<dt>
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<code class="parameter">cost_del</code></dt>
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<dd>
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<p class="para">
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定义删除次数
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</p>
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</dd>
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</dl>
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</p>
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</div>
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<div class="refsect1 returnvalues" id="refsect1-function.levenshtein-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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此函数返回两个字符串参数之间的编辑距离，如果其中一个字符串参数长度大于限制的255个字符时，返回-1。
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.levenshtein-examples">
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<h3 class="title">范例</h3>
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<p class="para">
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<div class="example" id="example-5917">
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<p><strong>Example #1 <span class="function"><strong>levenshtein()</strong></span> 例子：</strong></p>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// 输入拼写错误的单词<br /></span><span style="color: #0000BB">$input </span><span style="color: #007700">= </span><span style="color: #DD0000">'carrrot'</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// 要检查的单词数组<br /></span><span style="color: #0000BB">$words </span><span style="color: #007700">= array(</span><span style="color: #DD0000">'apple'</span><span style="color: #007700">,</span><span style="color: #DD0000">'pineapple'</span><span style="color: #007700">,</span><span style="color: #DD0000">'banana'</span><span style="color: #007700">,</span><span style="color: #DD0000">'orange'</span><span style="color: #007700">,<br /> </span><span style="color: #DD0000">'radish'</span><span style="color: #007700">,</span><span style="color: #DD0000">'carrot'</span><span style="color: #007700">,</span><span style="color: #DD0000">'pea'</span><span style="color: #007700">,</span><span style="color: #DD0000">'bean'</span><span style="color: #007700">,</span><span style="color: #DD0000">'potato'</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// 目前没有找到最短距离<br /></span><span style="color: #0000BB">$shortest </span><span style="color: #007700">= -</span><span style="color: #0000BB">1</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// 遍历单词来找到最接近的<br /></span><span style="color: #007700">foreach (</span><span style="color: #0000BB">$words </span><span style="color: #007700">as </span><span style="color: #0000BB">$word</span><span style="color: #007700">) {<br /><br /> </span><span style="color: #FF8000">// 计算输入单词与当前单词的距离<br /> </span><span style="color: #0000BB">$lev </span><span style="color: #007700">= </span><span style="color: #0000BB">levenshtein</span><span style="color: #007700">(</span><span style="color: #0000BB">$input</span><span style="color: #007700">, </span><span style="color: #0000BB">$word</span><span style="color: #007700">);<br /><br /> </span><span style="color: #FF8000">// 检查完全的匹配<br /> </span><span style="color: #007700">if (</span><span style="color: #0000BB">$lev </span><span style="color: #007700">== </span><span style="color: #0000BB">0</span><span style="color: #007700">) {<br /><br /> </span><span style="color: #FF8000">// 最接近的单词是这个（完全匹配）<br /> </span><span style="color: #0000BB">$closest </span><span style="color: #007700">= </span><span style="color: #0000BB">$word</span><span style="color: #007700">;<br /> </span><span style="color: #0000BB">$shortest </span><span style="color: #007700">= </span><span style="color: #0000BB">0</span><span style="color: #007700">;<br /><br /> </span><span style="color: #FF8000">// 退出循环；我们已经找到一个完全的匹配<br /> </span><span style="color: #007700">break;<br /> }<br /><br /> </span><span style="color: #FF8000">// 如果此次距离比上次找到的要短<br /> // 或者还没找到接近的单词<br /> </span><span style="color: #007700">if (</span><span style="color: #0000BB">$lev </span><span style="color: #007700"><= </span><span style="color: #0000BB">$shortest </span><span style="color: #007700">|| </span><span style="color: #0000BB">$shortest </span><span style="color: #007700">< </span><span style="color: #0000BB">0</span><span style="color: #007700">) {<br /> </span><span style="color: #FF8000">// 设置最接近的匹配以及它的最短距离<br /> </span><span style="color: #0000BB">$closest </span><span style="color: #007700">= </span><span style="color: #0000BB">$word</span><span style="color: #007700">;<br /> </span><span style="color: #0000BB">$shortest </span><span style="color: #007700">= </span><span style="color: #0000BB">$lev</span><span style="color: #007700">;<br /> }<br />}<br /><br />echo </span><span style="color: #DD0000">"Input word: </span><span style="color: #0000BB">$input</span><span style="color: #DD0000">\n"</span><span style="color: #007700">;<br />if (</span><span style="color: #0000BB">$shortest </span><span style="color: #007700">== </span><span style="color: #0000BB">0</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"Exact match found: </span><span style="color: #0000BB">$closest</span><span style="color: #DD0000">\n"</span><span style="color: #007700">;<br />} else {<br /> echo </span><span style="color: #DD0000">"Did you mean: </span><span style="color: #0000BB">$closest</span><span style="color: #DD0000">?\n"</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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<div class="example-contents"><p>以上例程会输出：</p></div>
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<div class="example-contents screen">
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<div class="cdata"><pre>
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Input word: carrrot
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Did you mean: carrot?
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</pre></div>
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</div>
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</div>
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</p>
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</div>
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<div class="refsect1 seealso" id="refsect1-function.levenshtein-seealso">
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<h3 class="title">参见</h3>
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<p class="para">
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<ul class="simplelist">
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<li class="member"><span class="function"><a href="soundex.html" class="function" rel="rdfs-seeAlso">soundex()</a> - Calculate the soundex key of a string</span></li>
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<li class="member"><span class="function"><a href="similar_text.html" class="function" rel="rdfs-seeAlso">similar_text()</a> - 计算两个字符串的相似度</span></li>
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<li class="member"><span class="function"><a href="metaphone.html" class="function" rel="rdfs-seeAlso">metaphone()</a> - Calculate the metaphone key of a string</span></li>
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</ul>
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</p>
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</div>
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</div></div></div></body></html> |