LongestParenthesis.py (using stack)

class Solution:
    def longestValidParentheses(self, s: str) -> int:
        stack = [-1] #initialize stack
        max_len = 0 #initialize length

        for i in range(len(s)): #loop in range the length of the given string
            if s[i] == "(": #check if first char is opening parenthesis
                stack.append(i) #append in stack
            else:
                stack.pop()
                if len(stack) == 0: #check for length
                    stack.append(i) #for empty stack
                else:
                    max_len = max(max_len, i - stack[-1]) #calculate max length
        
        return max_len