public int[] addAll(Collection<? extends T> items) {
    int[] indices = new int[items.size()];
    int i = 0;
    for (T item : items) {
      int newIndex = add(item);
      for (int j = 0; j < i; j++) {
        if (indices[j] >= newIndex) indices[j]++;
      }
      indices[i] = newIndex;
      i++;
    }
    return indices;
  }
public int[] addAll(Collection<? extends T> items)