32. 最长有效括号 - 力扣（LeetCode）

class Solution:
    def longestValidParentheses(self, s: str) -> int:
        stack = [-1]  # 存储索引，初始值 -1 代表“未匹配起点”
        max_length = 0

        for i, char in enumerate(s):
            if char == '(':
                stack.append(i)
            else:  # char == ')'
                stack.pop()
                if stack:
                    max_length = max(max_length, i - stack[-1])
                else:
                    stack.append(i)  # 记录新的无效起点

        return max_length