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Solution: Longest Valid Parentheses

Discover how to identify the longest well-formed parentheses substring by applying the stack pattern. This lesson teaches you to track indexes for matching pairs and calculate substring lengths efficiently using a single pass through the string.

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.

Constraints:

  • 00 \leq s.length 3×103\leq 3 ...