longestValidParentheses_better.py

def longestValidParentheses(s: str) -> int:
    def longest_from(i: int) -> int:
        longest = 0
        opened = 0
        for j in range(i, len(s)):
            if s[j] == '(':
                opened += 1
            elif opened > 0:
                opened -= 1
                if opened == 0:
                    longest = j - i + 1
            else:
                return longest
        return longest

    max_len = 0
    for i in range(len(s)):
        max_len = max(max_len, longest_from(i))
    return max_len