public static boolean isUniqueChars2(String s){
		if(s == null)
			return false;
		
		int flag = 0;
		for(int i = 0; i< s.length(); i++) {
			int offset = s.charAt(i) - 'a';
			
			if((flag & (1<<offset)) != 0)
				return false;
			else
				flag = flag | (1<<offset);
		}
		
		return true;
	}