/*

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, 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_HH

#define REVERSE_BFS_HH

#include <queue>

#include <marci_graph_traits.hh>

#include <marciMap.hh>

namespace  marci {

  template <typename graph_type>

  class reverse_bfs {

    typedef typename graph_traits<graph_type>::NodeIt NodeIt;

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

    typedef typename graph_traits<graph_type>::EachNodeIt EachNodeIt;

    typedef typename graph_traits<graph_type>::InEdgeIt InEdgeIt;

    graph_type& G;

    NodeIt t;

//    NodeMap<graph_type, EdgeIt> pred;

    NodeMap<graph_type, int> distance;

  public :

    /*

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

    */

    reverse_bfs(graph_type& _G, NodeIt _t) : G(_G), t(_t), distance(G, number_of(G.first_Node())) {

      distance.put(t,0);

    }

    void run() {

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

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

	    reached.put(w, true);

	  }

	}

      }

    }

    int dist(NodeIt v) {

      return distance.get(v);

    }

  };

} // namespace hugo

#endif //REVERSE_BFS_HH