Find the longest common substring using PHP

I recently found a need to find the longest common substring in an array of strings in PHP. A couple of Google searches didn’t return any relevant solutions, so I decided to roll my own. I haven’t benchmarked this yet for large strings and/or arrays, but it does what I needed it to for my own purpose.

[gist id=1021218 file=longest_common_substring.php]


[gist id=1021218 file=longest_common_substring_example.php]

One thought on “0

  1. A little bit simpler solution, only for two strings.
    It returns string.

    function longestCommonSubstring( $str1, $str2, $case_sensitive=false)
    $ret = array();

    $len1 = mb_strlen($str1);
    $len2 = mb_strlen($str2);
    if (! $len1 || ! $len2)
    return false;

    // Find shorter
    if ($len2 < $len1)
    $t = $len1;
    $len1 = $len2;
    $len2 = $t;
    $t = $str1;
    $str1 = $str2;
    $str2 = $t;

    if (! $case_sensitive)
    $str1 = mb_strtolower($str1);
    $str2 = mb_strtolower($str2);

    // Through chars.
    for ($i = 0; $i<$len1; $i++)
    // Next char is same?
    $c1 = mb_substr($str1, $i, 1);
    if ($c1 === mb_substr($str2, $i, 1))
    $ret[] = $c1;


    return implode('', $ret);

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