32. Longest Valid Parentheses - LeetCode Solution

class Solution:
    def longestValidParentheses(self, s: str) -> int:
        m = 0
        
        stack = [-1]
        
        for i in range(len(s)):
            if s[i] == "(":
                stack.append(i)
            else:
                stack.pop()
                if (len(stack) == 0):
                    stack.append(i)
                else:
                    m = max(m, i-stack[-1])
        
        return m