Solution: Longest Valid Parentheses
Explore how to use the stack data structure to identify the longest valid substring of well-formed parentheses in a given string. Learn to track unmatched parentheses using an index-based stack, optimize with a single pass solution, and understand the time and space complexity of this algorithm in C++. This lesson helps you apply stack patterns to real coding interview problems involving matching parentheses.
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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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