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Problem: Longest Valid Parentheses

Understand how to determine the longest well-formed parentheses substring in a string using stacks. Learn to track indices for efficient computation, handle unmatched parentheses, and implement this approach with O(n) time and space complexity.

Statement

Given a string s consisting solely of the characters '(' and ')', determine the length of the longest valid (well-formed) parentheses substring contained within s.

A valid parentheses substring is one in which every opening parenthesis '(' has a corresponding closing parenthesis ')', and the pairs are properly nested.

Constraints:

  • 00 \leq s.length 3×104\leq 3 \times 10^4 ...