public class Solution
extends Object
32 - Longest Valid Parentheses\.
Hard
Given a string containing just the characters `'('` and `')'`, find the length of the longest valid (well-formed) parentheses substring.
**Example 1:**
**Input:** s = "(()"
**Output:** 2
**Explanation:** The longest valid parentheses substring is "()".
**Example 2:**
**Input:** s = ")()())"
**Output:** 4
**Explanation:** The longest valid parentheses substring is "()()".
**Example 3:**
**Input:** s = ""
**Output:** 0
**Constraints:**
* 0 <= s.length <= 3 * 104
* `s[i]` is `'('`, or `')'`.