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如何在PHP中找到两个字符串之间最大的公共子字符串?

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Tom · 技术社区 · 16 年前

有没有一种快速算法可以在两个字符串中找到最大的公共子字符串 strings 或者这是一个完全的问题?

在PHP中,我可以大海捞针:

<?php

if (strstr("there is a needle in a haystack", "needle")) {
    echo "found<br>\n";
}
?>

但那将是非常昂贵的!特别是因为我的应用程序是搜索电子邮件数据库并查找垃圾邮件(即同一个人发送的类似电子邮件)。

有没有人可以把PHP代码扔出去?

6 回复 | 直到 8 年前

Zoredache 16 年前

这个 similar_text

这将计算两个字符串之间的相似性。返回两个字符串中匹配的字符数

你可能还想看看 levenshtein

Jeff Atwood 16 年前

http://www.devshed.com/c/a/PHP/Implement-Bayesian-inference-using-PHP-Part-1/

Ben 8 年前

我刚刚编写了一个函数,用于查找str1中存在于str2中的最长子字符串

public static function getLongestMatchingSubstring($str1, $str2)
{
    $len_1 = strlen($str1);
    $longest = '';
    for($i = 0; $i < $len_1; $i++){
        for($j = $len_1 - $i; $j > 0; $j--){
            $sub = substr($str1, $i, $j);
            if (strpos($str2, $sub) !== false && strlen($sub) > strlen($longest)){
                $longest = $sub;
                break;
            }
        }
    }
    return $longest;
}

Manoj Sharma 7 年前

例子:

$array = array(
    'PTT757LP4',
    'PTT757A',
    'PCT757B',
    'PCT757LP4EV'
);
echo longest_common_substring($array); // => T757

职能:

function longest_common_substring($words) {
    $words = array_map('strtolower', array_map('trim', $words));
    $sort_by_strlen = create_function('$a, $b', 'if (strlen($a) == strlen($b)) { return strcmp($a, $b); } return (strlen($a) < strlen($b)) ? -1 : 1;');
    usort($words, $sort_by_strlen);
    // We have to assume that each string has something in common with the first
    // string (post sort), we just need to figure out what the longest common
    // string is. If any string DOES NOT have something in common with the first
    // string, return false.
    $longest_common_substring = array();
    $shortest_string = str_split(array_shift($words));

    while (sizeof($shortest_string)) {
        array_unshift($longest_common_substring, '');
        foreach ($shortest_string as $ci => $char) {
            foreach ($words as $wi => $word) {
                if (!strstr($word, $longest_common_substring[0] . $char)) {
                    // No match
                    break 2;
                } // if
            } // foreach
            // we found the current char in each word, so add it to the first longest_common_substring element,
            // then start checking again using the next char as well
            $longest_common_substring[0].= $char;
        } // foreach
        // We've finished looping through the entire shortest_string.
        // Remove the first char and start all over. Do this until there are no more
        // chars to search on.
        array_shift($shortest_string);
    }
    // If we made it here then we've run through everything
    usort($longest_common_substring, $sort_by_strlen);
    return array_pop($longest_common_substring);
}

我在我的博客上写了一点:

Find the longest common substring using PHP (2011年2月24日)

Tanj 15 年前

后来我发现 a relevant wikipedia article

在PHP中,我找到了 similar_text 注意:类似这样的东西是不可伸缩的 :

<?php
// Gather all messages by a user into two identical associative arrays
$getMsgsRes = mysql_query(SELECT * FROM email_messages WHERE from = '$someUserID');
while($msgInfo = mysql_fetch_assoc($getMsgsRes))
{
    $msgsInfo1[] = $msgInfo;
    $msgsInfo2[] = $msgInfo;
}

// Loop over msgs and compare each one to every other
foreach ($msgsInfo1 as $msg1)
    foreach ($msgsInfo2 as $msg2)
        similar_text($msg1['msgTxt'],$msg2['msgTxt'],$similarity_pst);
        if ($similarity_pst > 90)
            echo "{$msg1['msgID']} is ${similarity_pst}% to {$msg2['msgID']}\n";
?>

Stefan Gehrig 16 年前

请看一看 Algorithm implementation/Strings/Longest common substring 在维基百科上。我还没有测试PHP实现,但它似乎与Wikipedia页面上的通用算法相匹配。