/* -*- C++ -*-

  * src/hugo/bfs.h - Part of HUGOlib, a generic C++ optimization library

  *

  * Copyright (C) 2004 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

  * (Egervary Combinatorial Optimization Research Group, EGRES).

  *

  * Permission to use, modify and distribute this software is granted

  * provided that this copyright notice appears in all copies. For

  * precise terms see the accompanying LICENSE file.

  *

  * This software is provided "AS IS" with no warranty of any kind,

  * express or implied, and with no claim as to its suitability for any

  * purpose.

  *

  */

 #ifndef HUGO_BFS_H

 #define HUGO_BFS_H

 ///\ingroup flowalgs

 ///\file

 ///\brief Bfs algorithm.

 ///

 ///\todo Revise Manual.

 #include <hugo/bin_heap.h>

 #include <hugo/invalid.h>

 namespace hugo {

 /// \addtogroup flowalgs

 /// @{

   ///%BFS algorithm class.

   ///This class provides an efficient implementation of %BFS algorithm.

   ///\param GR The graph type the algorithm runs on.

   ///This class does the same as Dijkstra does with constant 1 edge length,

   ///but it is faster.

   ///

   ///\author Alpar Juttner

 #ifdef DOXYGEN

   template <typename GR>

 #else

   template <typename GR>

 #endif

   class Bfs{

   public:

     ///The type of the underlying graph.

     typedef GR Graph;

     ///.

     typedef typename Graph::Node Node;

     ///.

     typedef typename Graph::NodeIt NodeIt;

     ///.

     typedef typename Graph::Edge Edge;

     ///.

     typedef typename Graph::OutEdgeIt OutEdgeIt;

     ///\brief The type of the map that stores the last

     ///edges of the shortest paths.

     typedef typename Graph::template NodeMap<Edge> PredMap;

     ///\brief The type of the map that stores the last but one

     ///nodes of the shortest paths.

     typedef typename Graph::template NodeMap<Node> PredNodeMap;

     ///The type of the map that stores the dists of the nodes.

     typedef typename Graph::template NodeMap<int> DistMap;

   private:

     /// Pointer to the underlying graph.

     const Graph *G;

     ///Pointer to the map of predecessors edges.

     PredMap *predecessor;

     ///Indicates if \ref predecessor is locally allocated (\c true) or not.

     bool local_predecessor;

     ///Pointer to the map of predecessors nodes.

     PredNodeMap *pred_node;

     ///Indicates if \ref pred_node is locally allocated (\c true) or not.

     bool local_pred_node;

     ///Pointer to the map of distances.

     DistMap *distance;

     ///Indicates if \ref distance is locally allocated (\c true) or not.

     bool local_distance;

     ///The source node of the last execution.

     Node source;

     ///Initializes the maps.

     void init_maps() 

     {

       if(!predecessor) {

 	local_predecessor = true;

 	predecessor = new PredMap(*G);

       }

       if(!pred_node) {

 	local_pred_node = true;

 	pred_node = new PredNodeMap(*G);

       }

       if(!distance) {

 	local_distance = true;

 	distance = new DistMap(*G);

       }

     }

   public :    

     ///Constructor.

     ///\param _G the graph the algorithm will run on.

     Bfs(const Graph& _G) :

       G(&_G),

       predecessor(NULL), local_predecessor(false),

       pred_node(NULL), local_pred_node(false),

       distance(NULL), local_distance(false)

     { }

     ///Destructor.

     ~Bfs() 

     {

       if(local_predecessor) delete predecessor;

       if(local_pred_node) delete pred_node;

       if(local_distance) delete distance;

     }

     ///Sets the map storing the predecessor edges.

     ///Sets the map storing the predecessor edges.

     ///If you don't use this function before calling \ref run(),

     ///it will allocate one. The destuctor deallocates this

     ///automatically allocated map, of course.

     ///\return <tt> (*this) </tt>

     Bfs &setPredMap(PredMap &m) 

     {

       if(local_predecessor) {

 	delete predecessor;

 	local_predecessor=false;

       }

       predecessor = &m;

       return *this;

     }

     ///Sets the map storing the predecessor nodes.

     ///Sets the map storing the predecessor nodes.

     ///If you don't use this function before calling \ref run(),

     ///it will allocate one. The destuctor deallocates this

     ///automatically allocated map, of course.

     ///\return <tt> (*this) </tt>

     Bfs &setPredNodeMap(PredNodeMap &m) 

     {

       if(local_pred_node) {

 	delete pred_node;

 	local_pred_node=false;

       }

       pred_node = &m;

       return *this;

     }

     ///Sets the map storing the distances calculated by the algorithm.

     ///Sets the map storing the distances calculated by the algorithm.

     ///If you don't use this function before calling \ref run(),

     ///it will allocate one. The destuctor deallocates this

     ///automatically allocated map, of course.

     ///\return <tt> (*this) </tt>

     Bfs &setDistMap(DistMap &m) 

     {

       if(local_distance) {

 	delete distance;

 	local_distance=false;

       }

       distance = &m;

       return *this;

     }

   ///Runs %BFS algorithm from node \c s.

   ///This method runs the %BFS algorithm from a root node \c s

   ///in order to

   ///compute a

   ///shortest path to each node. The algorithm computes

   ///- The %BFS tree.

   ///- The distance of each node from the root.

     void run(Node s) {

       init_maps();

       source = s;

       for ( NodeIt u(*G) ; u!=INVALID ; ++u ) {

 	predecessor->set(u,INVALID);

 	pred_node->set(u,INVALID);

       }

       int N=G->nodeNum();

       std::vector<typename Graph::Node> Q(N);

       int Qh=0;

       int Qt=0;

       Q[Qh++]=source;

       distance->set(s, 0);

       do {

 	Node m;

 	Node n=Q[Qt++];

 	int d= (*distance)[n]+1;

 	for(OutEdgeIt e(*G,n);e!=INVALID;++e)

 	  if((m=G->head(e))!=s && (*predecessor)[m]==INVALID) {

 	    Q[Qh++]=m;

 	    predecessor->set(m,e);

 	    pred_node->set(m,n);

 	    distance->set(m,d);

 	  }

       } while(Qt!=Qh);

     }

     ///The distance of a node from the root.

     ///Returns the distance of a node from the root.

     ///\pre \ref run() must be called before using this function.

     ///\warning If node \c v in unreachable from the root the return value

     ///of this funcion is undefined.

     int dist(Node v) const { return (*distance)[v]; }

     ///Returns the 'previous edge' of the %BFS path tree.

     ///For a node \c v it returns the 'previous edge' of the %BFS tree,

     ///i.e. it returns the last edge of a shortest path from the root to \c

     ///v. It is \ref INVALID

     ///if \c v is unreachable from the root or if \c v=s. The

     ///%BFS tree used here is equal to the %BFS tree used in

     ///\ref predNode(Node v).  \pre \ref run() must be called before using

     ///this function.

     Edge pred(Node v) const { return (*predecessor)[v]; }

     ///Returns the 'previous node' of the %BFS tree.

     ///For a node \c v it returns the 'previous node' on the %BFS tree,

     ///i.e. it returns the last but one node from a shortest path from the

     ///root to \c /v. It is INVALID if \c v is unreachable from the root or if

     ///\c v=s. The shortest path tree used here is equal to the %BFS

     ///tree used in \ref pred(Node v).  \pre \ref run() must be called before

     ///using this function.

     Node predNode(Node v) const { return (*pred_node)[v]; }

     ///Returns a reference to the NodeMap of distances.

     ///Returns a reference to the NodeMap of distances. \pre \ref run() must

     ///be called before using this function.

     const DistMap &distMap() const { return *distance;}

     ///Returns a reference to the %BFS tree map.

     ///Returns a reference to the NodeMap of the edges of the

     ///%BFS tree.

     ///\pre \ref run() must be called before using this function.

     const PredMap &predMap() const { return *predecessor;}

     ///Returns a reference to the map of last but one nodes of shortest paths.

     ///Returns a reference to the NodeMap of the last but one nodes on the

     ///%BFS tree.

     ///\pre \ref run() must be called before using this function.

     const PredNodeMap &predNodeMap() const { return *pred_node;}

     ///Checks if a node is reachable from the root.

     ///Returns \c true if \c v is reachable from the root.

     ///\note The root node is reported to be reached!

     ///

     ///\pre \ref run() must be called before using this function.

     ///

     bool reached(Node v) { return v==source || (*predecessor)[v]!=INVALID; }

   };

 /// @}

 } //END OF NAMESPACE HUGO

 #endif