diff algo

$trace = [];

        $str1 = 'bcadb';
        $N = strlen($str1);

        $str2 = 'acdb';
        $M = strlen($str2);

        $MAX = $N + $M;
        echo 'MAX=' . $MAX . PHP_EOL;
        $lengthOfSES = 0;

        $V[1] = 0;
        for ($D = 0; $D <= $MAX; $D++) {
            echo 'D=' . $D . PHP_EOL;
            for ($k = -$D; $k <= $D; $k += 2) {
                echo '  k=' . $k . PHP_EOL;
                if ($k == -$D || ($k != $D && $V[$k - 1] < $V[$k + 1])) {
                    $x = $V[$k + 1];
                } else {
                    $x = $V[$k - 1] + 1;
                }
                $y = $x - $k;
                while ($x < $N && $y < $M && ($str1[$x - 1 + 1] == $str2[$y - 1 + 1])) {
                    $x++;
                    $y++;
                }
                $V[$k] = $x;
                if ($x >= $N && $y >= $M) {
                    $lengthOfSES = $D;
                    print_r($V);
                    echo '$lengthOfSES is ' . $D . PHP_EOL;
                    die;
                }
            }
        }
        print('Length of an SES is greater than MAX');

    }