1 class Solution {
2 public int longestValidParentheses(String s) {
3 if(s.length() == 0) return 0;
4 char[] arr = s.toCharArray();
5 Stack<Integer> stack = new Stack<>();
6 int max = 0;
7 for(int i = 0; i < s.length(); i++){
8 char c = s.charAt(i);
9 if(c == '('){
10 stack.push(i);
11 }else if(c == ')' && !stack.isEmpty() && s.charAt(stack.peek()) == '('){
12 stack.pop();
13 }else{
14 stack.push(i);
15 }
16 }
17 if(stack.isEmpty()) return s.length();
18 int a = s.length();
19 while(!stack.isEmpty()){
20 int b = stack.pop();
21 max = Math.max(max, a-b-1);
22 a = b;
23 }
24 max = Math.max(a, max);
25 return max;
26
27
28 }
29 }
