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🔥Longest Valid Parentheses: Stack Boundary DPHard
SUPER HARD PROBLEM OF THE DAY+150 XP • FAANG OA TIER

High-difficulty challenge matching authentic Google, Amazon & Uber L5 online assessment conditions.

HardStack•Acceptance: 34.1%

Longest Valid Parentheses: Stack Boundary DP

Targeted in FAANG & Tech OA:MicrosoftGoogleAmazon
Real-World Engineering Context
Used in compiler frontends (LLVM, V8) and code formatters (Prettier) to locate well-balanced syntactic blocks and isolate bracket parsing errors.
Given a string containing just the characters `'('` and `')'`, return the length of the longest valid (well-formed) parentheses substring.

Sample Test Cases

Input: ["(()"]
Expected: 2
Input: [")()())"]
Expected: 4
Input: [""]
Expected: 0

Constraints

  • 0 <= s.length <= 3 * 10^4
  • s[i] is '(' or ')'.
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