/*

 reverse_bfs

 by jacint

 Performs a bfs on the out edges. It does not count predecessors, 

 only the distances, but one can easily modify it to know the pred as well.

 Constructor: 

 reverse_bfs(graph_type& G, node_iterator t)

 Member functions:

 void run(): runs a reverse bfs from t

   The following function should be used after run() was already run.

 int dist(node_iterator v) : returns the distance from v to t. It is the number of nodes if t is not reachable from v.

 */

 #ifndef REVERSE_BFS_HH

 #define REVERSE_BFS_HH

 #include <queue>

 #include <marci_graph_traits.hh>

 #include <marci_property_vector.hh>

 namespace  marci {

   template <typename graph_type>

   class reverse_bfs {

     typedef typename graph_traits<graph_type>::node_iterator node_iterator;

     //typedef typename graph_traits<graph_type>::edge_iterator edge_iterator;

     typedef typename graph_traits<graph_type>::each_node_iterator each_node_iterator;

     typedef typename graph_traits<graph_type>::in_edge_iterator in_edge_iterator;

     graph_type& G;

     node_iterator t;

 //    node_property_vector<graph_type, edge_iterator> pred;

     node_property_vector<graph_type, int> distance;

   public :

     /*

       The distance of the nodes is n, except t for which it is 0.

     */

     reverse_bfs(graph_type& _G, node_iterator _t) : G(_G), t(_t), distance(G, number_of(G.first_node())) {

       distance.put(t,0);

     }

     void run() {

       node_property_vector<graph_type, bool> reached(G, false); 

       reached.put(t, true);

       std::queue<node_iterator> bfs_queue;

       bfs_queue.push(t);

       while (!bfs_queue.empty()) {

         node_iterator v=bfs_queue.front();	

 	bfs_queue.pop();

 	for(in_edge_iterator e=G.first_in_edge(v); e.valid(); ++e) {

 	  node_iterator w=G.tail(e);

 	  if (!reached.get(w)) {

 	    bfs_queue.push(w);

 	    distance.put(w, distance.get(v)+1);

 	    reached.put(w, true);

 	  }

 	}

       }

     }

     int dist(node_iterator v) {

       return distance.get(v);

     }

   };

 } // namespace marci

 #endif //REVERSE_BFS_HH