/// <summary>
 /// Merge other <see cref="Treap{T} "/> into current one and clear other treap.
 /// </summary>
 /// <param name="other">Treap to be merged in.</param>
 /// <remarks> This method is O(Mlog(N/M)) operation.</remarks>
 public void MergeIn(Treap <T> other)
 {
     if (other.Count == 0)
     {
         return;
     }
     _version++;
     _root = Unite(_root, other._root);
     other.Clear();
 }