Solution: Longest Valid Parentheses
Explore how to apply the stack pattern to find the longest well-formed parentheses substring in a string. Learn to track indices to calculate valid substring lengths, handle unmatched parentheses, and implement an O(n) solution with clear time and space tradeoffs.
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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:
Every opening parenthesis ‘
(’ has a corresponding closing parenthesis ‘)’.The pairs of parentheses are correctly nested.
Return the length of this longest valid substring.
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