private List<String> shuffle(List<String> list) {
      List<String> listCopy = Lists.newArrayList(list);
      Random rnd = new Random();
      List<String> res = Lists.newArrayList();
      while (!listCopy.isEmpty()) {
        int index = rnd.nextInt(listCopy.size());
        res.add(listCopy.remove(index));
      }
      return res;
    }