Valid Parentheses

https://leetcode.com/problems/valid-parentheses/

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

 1 import java.util.HashMap;
 2 import java.util.HashSet;
 3 import java.util.Map;
 4 import java.util.Set;
 5 import java.util.Stack;
 6 
 7 
 8 public class Solution {
 9     public static boolean isValid(String s) {
10         int len=s.length();
11         Stack<Character> stack=new Stack();
12         Set<Character> l=new HashSet();
13         Set<Character> r=new HashSet();
14         Map<Character,Character> map=new HashMap();
15         l.add('(');l.add('[');l.add('{');
16         r.add(')');r.add(']');r.add('}');
17         map.put('{', '}');map.put('(', ')');map.put('[', ']');
18         for(int i=0;i<len;i++){
19             char c=s.charAt(i);
20             if(l.contains(c)){
21             stack.add(c);
22             }
23             else if(r.contains(c)){
24             if(stack.isEmpty()||map.get(stack.peek())!=c){return false;}
25             stack.pop();
26             }
27             else{return false;}
28         }
29         if(!stack.isEmpty()){return false;}
30         else{return true;}
31     }
32     public static void main(String[]args){
33     System.out.println(isValid("{{}}"));
34     }
35 }