[Lemon-commits] [lemon_svn] jacint: r35 - hugo/trunk/src/work

[Lemon SVN]

Author: jacint
Date: Tue Jan 20 22:27:28 2004
New Revision: 35

Added:
   hugo/trunk/src/work/reverse_bfs.hh

Log:
A reverse bfs


Added: hugo/trunk/src/work/reverse_bfs.hh
==============================================================================
--- (empty file)
+++ hugo/trunk/src/work/reverse_bfs.hh	Tue Jan 20 22:27:28 2004
@@ -0,0 +1,94 @@
+/*
+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.is_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
+
+