n_nodes( 0 ), n_edges( 0 )

{

ifstream ifs( file.c_str() );

if( ifs.fail() ) {

cerr << "could not open input file " << file << "\n";

exit( -1 );

}

cout << "Reading instance from file " << file << "\n";

ifs >> n_nodes >> n_edges;

cout << "Number of nodes: " << n_nodes << "\n";

cout << "Number of edges: " << n_edges << "\n";

edges.resize( n_edges );

incidentEdges.resize( n_nodes );

unsigned int id;

while( ifs >> id ) {

ifs >> edges[id].v1 >> edges[id].v2 >> edges[id].weight;

incidentEdges[edges[id].v1].push_back( id );

incidentEdges[edges[id].v2].push_back( id );

}

ifs.close();

cout << "Incidency list:" << "\n";

for( unsigned int v = 0; v < n_nodes; v++ ) {

cout << v << ": ";

for( auto& e : incidentEdges[v] ) {

cout << "(" << edges[e].v1 << "," << edges[e].v2 << "), ";

}

cout << "\n";

}