////   This file contains the C++ code from Program 9.4 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C++"//   by Bruno R. Preiss.////   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm09_04.cpp//void Tree::BreadthFirstTraversal (Visitor& visitor) const{    Queue& queue = *new QueueAsLinkedList ();    queue.RescindOwnership ();    if (!IsEmpty ())	queue.Enqueue (const_cast<Tree&> (*this));    while (!queue.IsEmpty () && !visitor.IsDone ())    {	Tree const& head =	    dynamic_cast<Tree const &> (queue.Dequeue ());	visitor.Visit (head.Key ());	for (unsigned int i = 0; i < head.Degree (); ++i)	{	    Tree& child = head.Subtree (i);	    if (!child.IsEmpty ())		queue.Enqueue (child);	}    }    delete &queue;}