[Solved] Given a string containing just the characters ‘(‘ and ‘)’, find the length of the longest valid (well-formed) parentheses substring.

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Question

Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.

Example 1:

Input: s = "(()"
Output: 2
Explanation: The longest valid parentheses substring is "()".

Example 2:

Input: s = ")()())"
Output: 4
Explanation: The longest valid parentheses substring is "()()".

Example 3:

Input: s = ""
Output: 0

Constraints:

  • 0 <= s.length <= 3 * 104
  • s[i] is '(', or ')'.

Python Solution

class Solution:
    def longestValidParentheses(self, s: str) -> int:
        stack = [-1]
        max_len = 0
        for p in range(len(s)):
            if s[p] == '(':
                stack.append(p)
            else:
                stack.pop()
                if stack == []:
                    stack.append(p)
                else:
                    max_len = max(p-stack[-1],max_len)
        return(max_len)
Abhishek Sharma
Abhishek Sharma

Started my Data Science journey in my 2nd year of college and since then continuously into it because of the magical powers of ML and continuously doing projects in almost every domain of AI like ML, DL, CV, NLP.

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