Graph1.cpp - Shortest path program using STL #pragma warning (disable: 4786) #include #include #include #include #include #include #include #include #include using namespace std; int INFINITY = INT_MAX; struct Vertex { string name; // Vertex name vector adj; // Adjacent vertices int dist; // Cost Vertex *path; // Previous vertex on shortest path Vertex( const string & nm ) : name( nm ) { reset( ); } void reset( ) { dist = INFINITY; path = NULL; } }; typedef map vmap; typedef pair vpair; class Graph { public: Graph( ) { } ~Graph( ); void addEdge( const string & sourceName, const string & destName ); void printPath( const string & destName ) const; void unweighted( const string & startName ); private: Vertex * getVertex( const string & vertexName ); void printPath( const Vertex & dest ) const; void clearAll( ); vmap vertexMap; vector allVertices; }; void Graph::addEdge( const string & sourceName, const string & destName ) { Vertex * v = getVertex( sourceName ); Vertex * w = getVertex( destName ); v->adj.push_back( w ); } void Graph::printPath( const string & destName ) const { vmap::const_iterator itr = vertexMap.find( destName ); if( itr == vertexMap.end( ) ) { cout << "Destination vertex not found" << endl; return; } const Vertex & w = *(*itr).second; if( w.dist == INFINITY ) cout << destName << " is unreachable"; else printPath( w ); cout << endl; } // If vertexName is not present, add it to vertexMap // In either case, return the Vertex Vertex * Graph::getVertex( const string & vertexName ) { vmap::iterator itr = vertexMap.find( vertexName ); if( itr == vertexMap.end( ) ) { Vertex *newv = new Vertex( vertexName ); allVertices.push_back( newv ); vertexMap.insert( vpair( vertexName, newv ) ); return newv; } return (*itr).second; } void Graph::printPath( const Vertex & dest ) const { if( dest.path != NULL ) { printPath( *dest.path ); cout << " to "; } cout << dest.name; } void Graph::clearAll( ) { for( int i = 0; i < allVertices.size( ); i++ ) allVertices[ i ]->reset( ); } Graph::~Graph( ) { for( int i = 0; i < allVertices.size( ); i++ ) delete allVertices[ i ]; } void Graph::unweighted( const string & startName ) { clearAll( ); vmap::iterator itr = vertexMap.find( startName ); if( itr == vertexMap.end( ) ) { cout << startName << " is not a vertex in this graph" << endl; return; } Vertex *start = (*itr).second; list q; q.push_back( start ); start->dist = 0; while( !q.empty( ) ) { Vertex *v = q.front( ); q.pop_front( ); for( int i = 0; i < v->adj.size( ); i++ ) { Vertex *w = v->adj[ i ]; if( w->dist == INFINITY ) { w->dist = v->dist + 1; w->path = v; q.push_back( w ); } } } } /** * Process a request; return false if end of file. */ bool processRequest( istream & in, Graph & g ) { string startName; string destName; cout << "Enter start node: "; if( !( in >> startName ) ) return false; cout << "Enter destination node: "; if( !( in >> destName ) ) return false; g.unweighted( startName ); g.printPath( destName ); return true; } /** * A simple main that reads the file given by argv[1] * and then calls processRequest to compute shortest paths. * Skimpy error checking in order to concentrate on the basics. */ int main( int argc, char *argv[ ] ) { Graph g; if( argc != 2 ) { cerr << "Usage: " << argv[ 0 ] << " graphfile" << endl; return 1; } ifstream inFile( argv[ 1 ] ); if( !inFile ) { cerr << "Cannot open " << argv[ 1 ] << endl; return 1; } string oneLine; // Read the words; add them to wordMap while( getline( inFile, oneLine ) ) { string source, dest; istringstream st( oneLine ); st >> source; st >> dest; g.addEdge( source, dest ); } cout << "File read" << endl; while( processRequest( cin, g ) ) ; return 0; }