php 用PHP求解最长公共子串问题

[php]代码库

<? php
class LCS {
    public static function main() {
        //设置字符串长度
        $substringLength1 = 20;
        $substringLength2 = 20;  //具体大小可自行设置
        $opt = array_fill(0, 21, array_fill(0, 21, null));

        // 随机生成字符串
        $x = self::GetRandomStrings($substringLength1);
        $y = self::GetRandomStrings($substringLength2);

        $startTime = microtime(true);

        // 动态规划计算所有子问题
        for ($i = $substringLength1 - 1; $i >= 0; $i--) {
            for ($j = $substringLength2 - 1; $j >= 0; $j--) {
                if ($x[$i] == $y[$j])
                    $opt[$i][$j] = $opt[$i + 1][$j + 1] + 1;
                else
                    $opt[$i][$j] = max($opt[$i + 1][$j], $opt[$i][$j + 1]);
            }
        }

        echo "substring1:".$x."\\r\\n";
        echo "substring2:".$y."\\r\\n";
        echo "LCS:";

        $i = 0;
        $j = 0;
        while ($i < $substringLength1 && $j < $substringLength2) {
            if ($x[$i] == $y[$j]) {
                echo $x[$i];
                $i++;
                $j++;
            } else if ($opt[$i + 1][$j] >= $opt[$i][$j + 1])
                $i++;
            else
                $j++;
        }

        $endTime = microtime(true);

        echo "\\r\\n";
        echo "Totle time is " . ($endTime - $startTime) . " s";
    }

    public static function GetRandomStrings($length) {
        $buffer = "abcdefghijklmnopqrstuvwxyz";
        $str = "";
        for($i = 0; $i < $length; $i++) {
            $random = rand(0, strlen($buffer) - 1);
            $str. = $buffer[$random];
        }
        return $str;
    }
}

LCS::main();
? >
//该片段来自于http://yuncode.net