/*

 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& G, NodeIt t)

 Member functions:

 void run(): runs a reverse bfs from t

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

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

 */

 #ifndef REVERSE_BFS_H

 #define REVERSE_BFS_H

 #include <queue>

 #include <list_graph.hh>

 namespace  marci {

   template <typename Graph>

   class reverse_bfs {

     typedef typename Graph::NodeIt NodeIt;

     typedef typename Graph::EachNodeIt EachNodeIt;

     typedef typename Graph::InEdgeIt InEdgeIt;

     Graph& G;

     NodeIt t;

     typename Graph::NodeMap<int> distance;

   public :

     /*

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

     */

     reverse_bfs(Graph& _G, NodeIt _t) : G(_G), t(_t), distance(G, G.nodeNum()) {

       distance.set(t,0);

     }

     void run() {

       typename Graph::NodeMap<bool> reached(G, false); 

       reached.set(t, true);

       std::queue<NodeIt> bfs_queue;

       bfs_queue.push(t);

       while (!bfs_queue.empty()) {

         NodeIt v=bfs_queue.front();	

 	bfs_queue.pop();

 	for(InEdgeIt e=G.template first<InEdgeIt>(v); e.valid(); ++e) {

 	  NodeIt w=G.tail(e);

 	  if (!reached.get(w)) {

 	    bfs_queue.push(w);

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

 	    reached.set(w, true);

 	  }

 	}

       }

     }

     int dist(NodeIt v) {

       return distance.get(v);

     }

   };

 } // namespace marci

 #endif //REVERSE_BFS_HH