public static boolean isUniqueChars(String s){
		if(s == null)
			return false;
		HashSet<Character> chars = new HashSet<Character>();
		for(int i = 0; i < s.length(); i++  ) {
			if(chars.contains(s.charAt(i)))
				return false;
			else
				chars.add(s.charAt(i));
		}
		return true;
	}