////   This file contains the C++ code from Program 11.7 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/pgm11_07.cpp//class LeftistHeap :    public BinaryTree, public MergeablePriorityQueue{    unsigned int nullPathLength;    void SwapContents (LeftistHeap&);public:    LeftistHeap ();    LeftistHeap (Object&);    LeftistHeap& Left () const;    LeftistHeap& Right () const;    void Merge (MergeablePriorityQueue&);    // ...};