balanced brackets java

// Program to check balanced brackets using stack

import java.util.Scanner;
import java.util.Stack;

/**
 * Created by MOHIT on 06-10-2016.
 */
public class BalancedBRackets {
    public static void main(String a[]){
        Scanner sc = new Scanner(System.in);
        int test = sc.nextInt();
        for(int i=0; i<test; i++){
            Stack s1 = new Stack();
            boolean flag = false;
            String str = sc.next();
            for (int j=0; j<str.length();j++){
                char s = str.charAt(j);
                if(s == '(' || s == '[' || s == '{'){
                    s1.push(s);
                }
                else if(s == ')'){
                    if (s1.size() > 0){
                        char temp = (char) s1.pop();
                        if(temp != '('){
                            flag = true;
                            break;
                        }
                    }
                    else{
                        flag = true;
                        break;
                    }
                }
                else if(s == ']'){
                    if (s1.size() > 0){
                        char temp = (char) s1.pop();
                        if(temp != '['){
                            flag = true;
                            break;
                        }
                    }
                    else{
                        flag = true;
                        break;
                    }
                }
                else if(s == '}'){
                    if (s1.size() > 0){
                        char temp = (char) s1.pop();
                        if(temp != '{'){
                            flag = true;
                            break;
                        }
                    }
                    else{
                        flag = true;
                        break;
                    }
                }
            }
            if(!flag && s1.size() == 0){
                System.out.println("YES");
            }else{
                System.out.println("NO");
            }
        }
    }
}

/*

Sample Input

3
{[()]}
{[(])}
{{[[(())]]}}


Sample Output

YES
NO
YES
*/