longestValidParentheses_naive.py

def longestValidParentheses(s: str) -> int:
    def is_valid(i: int, j: int) -> bool:
        opened = 0
        for c in s[i:j+1]:
            if c == '(':
                opened += 1
            elif opened > 0:
                opened -= 1
            else:
                return False
        return opened == 0

    max_len = 0
    for i in range(len(s)):
        for j in range(len(s)):
            if is_valid(i, j):
                max_len = max(max_len, j - i + 1)
    return max_len