A bracket is considered to be any one of the following characters: ( ) { } [ or ].

Two brackets are a matched pair if the an opening bracket i.e. ( [ or { occurs to the left of a closing bracket i.e. ) ] or } of the same type. There are three types of matched pairs of brackets: [], {}, and ().

A matching pair of brackets is not balanced if the set of brackets it encloses are not matched. For example, {[(])} is not balanced because the contents in between { and } are not balanced. The pair of square brackets encloses a single, unbalanced opening bracket, (, and the pair of parentheses encloses a single, unbalanced closing square bracket, ].

By this logic, we say a sequence of brackets is balanced if the following conditions are met:

It contains no unmatched brackets.
The subset of brackets enclosed within the confines of a matched pair of brackets is also a matched pair of brackets.
Given strings of brackets, determine whether each sequence of brackets is balanced. If a string is balanced, return YES. Otherwise, return NO.

Function Description - Complete the function isBalanced in the editor below.

isBalanced has the following parameter(s):
s: a string of brackets

Constraints
All characters are in the sequences { } ( ) and [ ].

Output Format
For each string, return YES or NO: YES if the sequence is balanced or NO if it is not.

Solution below

import java.util.*;
import org.junit.*;
import org.junit.runner.*;
import static org.junit.Assert.*;

public class Solution {
    private static String isBalanced(String s){
      while(s.contains("()") || s.contains("[]") || s.contains("{}")) {
          s = s.replace("()", "").replace("[]", "").replace("{}", "");
      }
      return s.isEmpty() ? "YES" : "NO";
    }

    public static void main(String[] args) {
        JUnitCore.main("Solution");
    }

    @Test
    public void test1() {
        String input = "{[()]}";
        String expected = "YES";
        String actual = isBalanced(input);
        assertEquals(expected, actual);
    }

    @Test
    public void test2() {
        String input = "{}[]";
        String expected = "YES";
        String actual = isBalanced(input);
        assertEquals(expected, actual);
    }

    @Test
    public void test3() {
      String input = "{[(])}";
      String expected = "NO";
      String actual = isBalanced(input);
      assertEquals(expected, actual);
    }

}