source: lemon-0.x/src/hugo/bfs.h @ 788:c3187cafcabf

// -*- C++ -*-
#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:
    const Graph *G;
    PredMap *predecessor;
    bool local_predecessor;
    PredNodeMap *pred_node;
    bool local_pred_node;
    DistMap *distance;
    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 :    
    Bfs(const Graph& _G) :
      G(&_G),
      predecessor(NULL), local_predecessor(false),
      pred_node(NULL), local_pred_node(false),
      distance(NULL), local_distance(false)
    { }
    
    ~Bfs() 
    {
      if(local_predecessor) delete predecessor;
      if(local_pred_node) delete pred_node;
      if(local_distance) delete distance;
    }

    ///Sets the graph the algorithm will run on.

    ///Sets the graph the algorithm will run on.
    ///\return <tt> (*this) </tt>
    ///\bug What about maps?
    ///\todo It may be unnecessary
    Bfs &setGraph(const Graph &_G) 
    {
      G = &_G;
      return *this;
    }
    ///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.
    ///\warning 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