jacint@78: /*
jacint@78: reverse_bfs
jacint@78: by jacint
jacint@78: Performs a bfs on the out Edges. It does not count predecessors, 
jacint@78: only the distances, but one can easily modify it to know the pred as well.
jacint@78: 
jacint@78: Constructor: 
jacint@78: 
jacint@78: reverse_bfs(Graph& G, NodeIt t)
jacint@78: 
jacint@78: 
jacint@78: 
jacint@78: Member functions:
jacint@78: 
jacint@78: void run(): runs a reverse bfs from t
jacint@78: 
jacint@78:   The following function should be used after run() was already run.
jacint@78: 
jacint@78: int dist(NodeIt v) : returns the distance from v to t. It is the number of nodes if t is not reachable from v.
jacint@78: 
jacint@78: */
jacint@78: #ifndef REVERSE_BFS_H
jacint@78: #define REVERSE_BFS_H
jacint@78: 
jacint@78: #include <queue>
jacint@78: #include <list_graph.hh>
jacint@78: 
jacint@78: 
jacint@78: namespace  marci {
jacint@78: 
jacint@78:   template <typename Graph>
jacint@78:   class reverse_bfs {
jacint@78:     typedef typename Graph::NodeIt NodeIt;
jacint@78:     typedef typename Graph::EachNodeIt EachNodeIt;
jacint@78:     typedef typename Graph::InEdgeIt InEdgeIt;
jacint@78: 
jacint@78: 
jacint@78:     Graph& G;
jacint@78:     NodeIt t;
jacint@78:     typename Graph::NodeMap<int> distance;
jacint@78:     
jacint@78: 
jacint@78:   public :
jacint@78: 
jacint@78:     /*
jacint@78:       The distance of the Nodes is n, except t for which it is 0.
jacint@78:     */
jacint@78:     reverse_bfs(Graph& _G, NodeIt _t) : G(_G), t(_t), distance(G, G.nodeNum()) {
jacint@78:       distance.set(t,0);
jacint@78:     }
jacint@78:     
jacint@78:     void run() {
jacint@78: 
jacint@78:       typename Graph::NodeMap<bool> reached(G, false); 
jacint@78:       reached.set(t, true);
jacint@78: 
jacint@78:       std::queue<NodeIt> bfs_queue;
jacint@78:       bfs_queue.push(t);
jacint@78: 
jacint@78:       while (!bfs_queue.empty()) {
jacint@78: 
jacint@78:         NodeIt v=bfs_queue.front();	
jacint@78: 	bfs_queue.pop();
jacint@78: 
jacint@78: 	for(InEdgeIt e=G.template first<InEdgeIt>(v); e.valid(); ++e) {
jacint@78: 	  NodeIt w=G.tail(e);
jacint@78: 	  if (!reached.get(w)) {
jacint@78: 	    bfs_queue.push(w);
jacint@78: 	    distance.set(w, distance.get(v)+1);
jacint@78: 	    reached.set(w, true);
jacint@78: 	  }
jacint@78: 	}
jacint@78:       }
jacint@78:     }
jacint@78: 
jacint@78: 
jacint@78: 
jacint@78:     int dist(NodeIt v) {
jacint@78:       return distance.get(v);
jacint@78:     }
jacint@78: 
jacint@78: 
jacint@78:   };
jacint@78: 
alpar@105: } // namespace hugo
jacint@78: 
jacint@78: #endif //REVERSE_BFS_HH
jacint@78: 
jacint@78: