Solution.java

import java.util.*;
class Solution{
	
	 public static void main(String[] args) {
 /* Create HashMap to match opening brackets with closing brackets */
 HashMap<Character, Character> map = new HashMap();
 map.put('(', ')');
 map.put('[', ']');
 map.put('{', '}');
 
 /* Test each expression for validity */
 Scanner scan = new Scanner(System.in);
 while (scan.hasNext()) {
 String expression = scan.next();
 System.out.println(isBalanced(expression, map) ? "true" : "false" );
 }
 scan.close();
 }
 
 private static boolean isBalanced(String expression, HashMap<Character, Character> map) {
 if ((expression.length() % 2) != 0) {
 return false; // odd length Strings are not balanced
 } 
 ArrayDeque<Character> deque = new ArrayDeque(); // use deque as a stack
 for (int i = 0; i < expression.length(); i++) {
 Character ch = expression.charAt(i);
 if (map.containsKey(ch)) {
 deque.push(ch);
 } else if (deque.isEmpty() || ch != map.get(deque.pop())) {
 return false;
 }
 }
 return deque.isEmpty();
 }

}