// returns a reference to the node at index k,
  // where the indexes are numbered 0 through size()-1
  // precondition:  0 <= k < size()
  private ListNode getKthNode(int k)
  {
    ListNode node = front;

    for (int count = 0; count < k; count++)
      node = node.getNext();

    return node;
  }

  // removes the last num nodes from other and attaches them
  // in the same order to the end of this WaitingList;
  // updates the number of nodes in each list to reflect the move
  // precondition:  size() > 0;
  //                0 < num <= other.size()
  public void transferNodesFromEnd(WaitingList other, int num)
  {
    ListNode tail = getKthNode(numNodes - 1);
    ListNode node = other.getKthNode(other.numNodes - num);

    if (other.numNodes == num)
      other.front = null;
    else
    {
      ListNode prev = other.getKthNode(other.numNodes - num - 1);
      prev.setNext(null);
    }

    tail.setNext(node);

    numNodes += num;
    other.numNodes -= num;
  }