[最大最长]最长有效括号的长度

class Solution:
    def longestValidParentheses(self, s: str) -> int:

        stack = [-1]
        max_len = 0

        for i in range(len(s)):
            if s[i] == "(":
                stack.append(i)
            elif s[i] == ")":
                if stack and stack[-1] != -1 and s[stack[-1]] == "(":
                    stack.pop(-1)
                    max_len = max(max_len, i - stack[-1])
                else:
                    stack.append(i)

        return max_len