两个字符串都存在的最长的相同的字符串

longestCommonSubstring.php

<?php
function longestCommonSubstring($str_a, $str_b, $case_sensitive = false)
{
    $len_a = mb_strlen($str_a);
    $len_b = mb_strlen($str_b);
    
    if (! $len_a || ! $len_b) {
        return false;
    }
    
    if ($len_b < $len_a) {
       list($len_a, $len_b) = array($len_b, $len_a);
       list($str_a, $str_b) = array($str_b, $str_a);
    }
    
    if (! $case_sensitive) {
        $str_a = strtolower($str_a);
        $str_b = strtolower($str_b);
    }
    
    $ret = array();
    array_unshift($ret, '');
    
    for ($i = 0; $i < $len_a; $i++) {
        $c = mb_substr($str_a, $i, 1);
        if ($c === mb_substr($str_b, $i, 1)) {
            $ret[0] .= $c
        } else {
            array_unshift($ret, '');
        }
    }
    
    usort($ret, function($a, $b) {
        if (mb_strlen($a) === mb_strlen($b)) {
            return strcmp($a, $b);
        }
        
        return mb_strlen($a) > mb_strlen($b) ? -1 : 1;
    });
    
    return array_pop($ret);
}