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Solution: Longest Valid Parentheses

Explore how to use the stack data structure to solve the longest valid parentheses substring problem efficiently. This lesson guides you through identifying matching pairs and calculating lengths using stack operations, helping you master a common interview coding pattern.

Statement

You are given a string composed entirely of ‘(’ and ‘)’ characters. Your goal is to identify the longest contiguous segment (substring) within this string that represents a “well-formed” or “valid” sequence of parentheses.

A substring is considered valid if:

  1. Every opening parenthesis ‘(’ has a corresponding closing parenthesis ‘)’.

  2. The pairs of parentheses are correctly nested.

Return the length of this longest valid substring.

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