无重复最小子串长度

function lengthOfLongestSubstring($s) {
        $len = strlen($s);
        if ($len == 1 || $len == 0) {
            return $len;
        }
        $map = array();
        $i = 0;
        $max = 0;
        for ($j = 0; $j < $len; $j++) {
            if (isset($map[$s[$j]])) {
                $i = max($map[$s[$j]] + 1, $i);
            }
            $map[$s[$j]] = $j;
            $max = max($max, $j - $i + 1);
        }

        return $max;

    }