undirected-graph-list.cpp

/*
  Adjacency List in Vector
*/

vector <vector <int> > adj_list;

int main(){
  int num_nodes, num_edges;
  cin >> num_nodes >> num_edges;
  adj_list.resize(num_nodes+1);
  for(int i = 0, u, v; i < num_edges; ++i){
    // take nodes between which we have an edge
    cin >> u >> v;
    // undirected so we push v to list of u and vice versa
    adj_list[u].push_back(v);
    adj_list[v].push_back(u);
  }
  // do something with the graph
}