20. Valid Parentheses

 1 class Solution {
 2     public boolean isValid(String s) {
 3         Stack<Character> stack = new Stack<Character>();
 4         char[] arr = s.toCharArray();
 5         for(char c : arr) {
 6             if(c == ‘(‘) {
 7                 stack.push(‘)‘);
 8             }else if(c == ‘{‘) {
 9                 stack.push(‘}‘);
10             }else if(c == ‘[‘) {
11                 stack.push(‘]‘);
12             }else if(stack.isEmpty() || stack.pop() != c) {
13                 return false;
14             }
15         }
16         return stack.isEmpty();
17         
18     }
19 }