////   This file contains the C++ code from Program 11.11 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_11.cpp//Object& LeftistHeap::DequeueMin (){    if (IsEmpty ())	throw domain_error ("priority queue is empty");    Object& result = *key;    LeftistHeap& oldLeft = Left ();    LeftistHeap& oldRight = Right ();    key = 0;    left = 0;    right = 0;    SwapContents (oldLeft);    delete &oldLeft;    Merge (oldRight);    delete &oldRight;    return result;}