/*

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