Leetcode : Longest Valid Parameter

Question:https://leetcode.com/problems/longest-valid-parentheses/

Solution:

class Solution:

    def longestValidParentheses(self, s: str) -> int:

        len_string = len(s)

        count = 0

        start_bracket = 0 ## (

        for index in range(0,len_string):

            if index==0:

                if s[index]=="(":

                    start_bracket +=1

                else:

                    continue

           

            elif s[index] == "(":

                if s[index-1] == "(":

                    start_bracket+=1

                else:

                    start_bracket =1

                   

            elif s[index]==")" and start_bracket > 0:

                count+=1

                start_bracket-=1

            else:

                continue

        return count*2

Notes:

Didn't understand the problem in the rightful manner, as things were not clear.