source: lemon-0.x/src/work/jacint/reverse_bfs.h @ 108:0351b00fd283

/*
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 hugo

#endif //REVERSE_BFS_HH