_32.java

package com.fishercoder.solutions;

import java.util.Stack;

public class _32 {
    public static class Solution1 {
        public int longestValidParentheses(String s) {
            int result = 0;
            Stack<Integer> stack = new Stack();
            stack.push(-1);
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == '(') {
                    stack.push(i);
                } else {
                    stack.pop();
                    if (stack.isEmpty()) {
                        stack.push(i);
                    } else {
                        result = Math.max(result, i - stack.peek());
                    }
                }
            }
            return result;
        }
    }
}