gistfile1.java

private String y = "Possible";
private String n = "Impossible";
	
	
	public String ableToSolve(String s) {
		if (s == null) return n;
		if (s.isEmpty()) return y;
		if (s.length() % 2 != 0) return n;
		
		Stack<Character> stack = new Stack<Character>();
		
		for(int i = 0; i < s.length(); ++i) {
			char c = s.charAt(i);
			if (!stack.isEmpty() && stack.peek().equals(c)) {
				stack.pop();
			} else {
				stack.push(c);
			}
		
		}
		
		return stack.isEmpty() ? y : n;
	}