List<Integer> input = new ArrayList<Integer>();
  Collections.sort(input);
  Set<Integer> result1 = new HashSet<Integer>();
  Set<Integer> result2 = new HashSet<Integer>();
  for (int i = 0; i < input.size(); i++) {
      if (i % 2 == 0) {// if i is even
          result1.add(input.get(i));
      } else {
          result2.add(input.get(i));
      }
  }