33. Longest Valid Parentheses

Hard · String

Given a string containing only characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.

A valid parentheses string is one where every opening bracket has a matching closing bracket in the correct order. For example, "()" and "(())" are valid, but ")()())" is not entirely valid (though it contains "()" as a valid substring).

Return the length of the longest contiguous substring that forms valid parentheses.

Examples

Example 1
Input: "(()"
Output: 2
Explanation: The longest valid parentheses substring is "()" with length 2.

Example 2
Input: ")()())"
Output: 4
Explanation: The longest valid parentheses substring is "()()" with length 4.

Constraints

• Standard input/output constraints apply