////   This file contains the C++ code from Program 16.7 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/pgm16_07.cpp//void Graph::DepthFirstTraversal (    PrePostVisitor& visitor, Vertex const& start) const{    Array<bool> visited (numberOfVertices);    for (Vertex::Number v = 0; v < numberOfVertices; ++v)	visited [v] = false;    DepthFirstTraversal (	visitor, const_cast<Vertex&> (start), visited);}void Graph::DepthFirstTraversal (PrePostVisitor& visitor,    Vertex& vertex, Array<bool>& visited) const{    if (visitor.IsDone ())	return;    visitor.PreVisit (vertex);    visited [vertex] = true;    Iterator& p = EmanatingEdges (vertex);    while (!p.IsDone ()) {	Edge& edge = dynamic_cast<Edge&> (*p);	Vertex& to = edge.Mate (vertex);	if (!visited [to])	    DepthFirstTraversal (visitor, to, visited);	++p;    }    delete &p;    visitor.PostVisit (vertex);}