src/hugo/bfs.h
author alpar
Mon, 13 Sep 2004 11:24:35 +0000
changeset 835 eb9587f09b42
parent 781 d4d182ab75bd
child 906 17f31d280385
permissions -rw-r--r--
Remove one remaining range checking.
     1 // -*- C++ -*-
     2 #ifndef HUGO_BFS_H
     3 #define HUGO_BFS_H
     4 
     5 ///\ingroup flowalgs
     6 ///\file
     7 ///\brief Bfs algorithm.
     8 ///
     9 ///\todo Revise Manual.
    10 
    11 #include <hugo/bin_heap.h>
    12 #include <hugo/invalid.h>
    13 
    14 namespace hugo {
    15 
    16 /// \addtogroup flowalgs
    17 /// @{
    18 
    19   ///%BFS algorithm class.
    20 
    21   ///This class provides an efficient implementation of %BFS algorithm.
    22   ///\param GR The graph type the algorithm runs on.
    23   ///This class does the same as Dijkstra does with constant 1 edge length,
    24   ///but it is faster.
    25   ///
    26   ///\author Alpar Juttner
    27 
    28 #ifdef DOXYGEN
    29   template <typename GR>
    30 #else
    31   template <typename GR>
    32 #endif
    33   class Bfs{
    34   public:
    35     ///The type of the underlying graph.
    36     typedef GR Graph;
    37     ///.
    38     typedef typename Graph::Node Node;
    39     ///.
    40     typedef typename Graph::NodeIt NodeIt;
    41     ///.
    42     typedef typename Graph::Edge Edge;
    43     ///.
    44     typedef typename Graph::OutEdgeIt OutEdgeIt;
    45     
    46     ///\brief The type of the map that stores the last
    47     ///edges of the shortest paths.
    48     typedef typename Graph::template NodeMap<Edge> PredMap;
    49     ///\brief The type of the map that stores the last but one
    50     ///nodes of the shortest paths.
    51     typedef typename Graph::template NodeMap<Node> PredNodeMap;
    52     ///The type of the map that stores the dists of the nodes.
    53     typedef typename Graph::template NodeMap<int> DistMap;
    54 
    55   private:
    56     /// Pointer to the underlying graph.
    57     const Graph *G;
    58     ///Pointer to the map of predecessors edges.
    59     PredMap *predecessor;
    60     ///Indicates if \ref predecessor is locally allocated (\c true) or not.
    61     bool local_predecessor;
    62     ///Pointer to the map of predecessors nodes.
    63     PredNodeMap *pred_node;
    64     ///Indicates if \ref pred_node is locally allocated (\c true) or not.
    65     bool local_pred_node;
    66     ///Pointer to the map of distances.
    67     DistMap *distance;
    68     ///Indicates if \ref distance is locally allocated (\c true) or not.
    69     bool local_distance;
    70 
    71     ///The source node of the last execution.
    72     Node source;
    73 
    74 
    75     ///Initializes the maps.
    76     void init_maps() 
    77     {
    78       if(!predecessor) {
    79 	local_predecessor = true;
    80 	predecessor = new PredMap(*G);
    81       }
    82       if(!pred_node) {
    83 	local_pred_node = true;
    84 	pred_node = new PredNodeMap(*G);
    85       }
    86       if(!distance) {
    87 	local_distance = true;
    88 	distance = new DistMap(*G);
    89       }
    90     }
    91     
    92   public :    
    93     ///Constructor.
    94     
    95     ///\param _G the graph the algorithm will run on.
    96     Bfs(const Graph& _G) :
    97       G(&_G),
    98       predecessor(NULL), local_predecessor(false),
    99       pred_node(NULL), local_pred_node(false),
   100       distance(NULL), local_distance(false)
   101     { }
   102     
   103     ///Destructor.
   104     ~Bfs() 
   105     {
   106       if(local_predecessor) delete predecessor;
   107       if(local_pred_node) delete pred_node;
   108       if(local_distance) delete distance;
   109     }
   110 
   111     ///Sets the map storing the predecessor edges.
   112 
   113     ///Sets the map storing the predecessor edges.
   114     ///If you don't use this function before calling \ref run(),
   115     ///it will allocate one. The destuctor deallocates this
   116     ///automatically allocated map, of course.
   117     ///\return <tt> (*this) </tt>
   118     Bfs &setPredMap(PredMap &m) 
   119     {
   120       if(local_predecessor) {
   121 	delete predecessor;
   122 	local_predecessor=false;
   123       }
   124       predecessor = &m;
   125       return *this;
   126     }
   127 
   128     ///Sets the map storing the predecessor nodes.
   129 
   130     ///Sets the map storing the predecessor nodes.
   131     ///If you don't use this function before calling \ref run(),
   132     ///it will allocate one. The destuctor deallocates this
   133     ///automatically allocated map, of course.
   134     ///\return <tt> (*this) </tt>
   135     Bfs &setPredNodeMap(PredNodeMap &m) 
   136     {
   137       if(local_pred_node) {
   138 	delete pred_node;
   139 	local_pred_node=false;
   140       }
   141       pred_node = &m;
   142       return *this;
   143     }
   144 
   145     ///Sets the map storing the distances calculated by the algorithm.
   146 
   147     ///Sets the map storing the distances calculated by the algorithm.
   148     ///If you don't use this function before calling \ref run(),
   149     ///it will allocate one. The destuctor deallocates this
   150     ///automatically allocated map, of course.
   151     ///\return <tt> (*this) </tt>
   152     Bfs &setDistMap(DistMap &m) 
   153     {
   154       if(local_distance) {
   155 	delete distance;
   156 	local_distance=false;
   157       }
   158       distance = &m;
   159       return *this;
   160     }
   161     
   162   ///Runs %BFS algorithm from node \c s.
   163 
   164   ///This method runs the %BFS algorithm from a root node \c s
   165   ///in order to
   166   ///compute a
   167   ///shortest path to each node. The algorithm computes
   168   ///- The %BFS tree.
   169   ///- The distance of each node from the root.
   170  
   171     void run(Node s) {
   172       
   173       init_maps();
   174       
   175       source = s;
   176       
   177       for ( NodeIt u(*G) ; u!=INVALID ; ++u ) {
   178 	predecessor->set(u,INVALID);
   179 	pred_node->set(u,INVALID);
   180       }
   181       
   182       int N=G->nodeNum();
   183       std::vector<typename Graph::Node> Q(N);
   184       int Qh=0;
   185       int Qt=0;
   186       
   187       Q[Qh++]=source;
   188       distance->set(s, 0);
   189       do {
   190 	Node m;
   191 	Node n=Q[Qt++];
   192 	int d= (*distance)[n]+1;
   193 	
   194 	for(OutEdgeIt e(*G,n);e!=INVALID;++e)
   195 	  if((m=G->head(e))!=s && (*predecessor)[m]==INVALID) {
   196 	    Q[Qh++]=m;
   197 	    predecessor->set(m,e);
   198 	    pred_node->set(m,n);
   199 	    distance->set(m,d);
   200 	  }
   201       } while(Qt!=Qh);
   202     }
   203     
   204     ///The distance of a node from the root.
   205 
   206     ///Returns the distance of a node from the root.
   207     ///\pre \ref run() must be called before using this function.
   208     ///\warning If node \c v in unreachable from the root the return value
   209     ///of this funcion is undefined.
   210     int dist(Node v) const { return (*distance)[v]; }
   211 
   212     ///Returns the 'previous edge' of the %BFS path tree.
   213 
   214     ///For a node \c v it returns the 'previous edge' of the %BFS tree,
   215     ///i.e. it returns the last edge of a shortest path from the root to \c
   216     ///v. It is \ref INVALID
   217     ///if \c v is unreachable from the root or if \c v=s. The
   218     ///%BFS tree used here is equal to the %BFS tree used in
   219     ///\ref predNode(Node v).  \pre \ref run() must be called before using
   220     ///this function.
   221     Edge pred(Node v) const { return (*predecessor)[v]; }
   222 
   223     ///Returns the 'previous node' of the %BFS tree.
   224 
   225     ///For a node \c v it returns the 'previous node' on the %BFS tree,
   226     ///i.e. it returns the last but one node from a shortest path from the
   227     ///root to \c /v. It is INVALID if \c v is unreachable from the root or if
   228     ///\c v=s. The shortest path tree used here is equal to the %BFS
   229     ///tree used in \ref pred(Node v).  \pre \ref run() must be called before
   230     ///using this function.
   231     Node predNode(Node v) const { return (*pred_node)[v]; }
   232     
   233     ///Returns a reference to the NodeMap of distances.
   234     
   235     ///Returns a reference to the NodeMap of distances. \pre \ref run() must
   236     ///be called before using this function.
   237     const DistMap &distMap() const { return *distance;}
   238  
   239     ///Returns a reference to the %BFS tree map.
   240 
   241     ///Returns a reference to the NodeMap of the edges of the
   242     ///%BFS tree.
   243     ///\pre \ref run() must be called before using this function.
   244     const PredMap &predMap() const { return *predecessor;}
   245  
   246     ///Returns a reference to the map of last but one nodes of shortest paths.
   247 
   248     ///Returns a reference to the NodeMap of the last but one nodes on the
   249     ///%BFS tree.
   250     ///\pre \ref run() must be called before using this function.
   251     const PredNodeMap &predNodeMap() const { return *pred_node;}
   252 
   253     ///Checks if a node is reachable from the root.
   254 
   255     ///Returns \c true if \c v is reachable from the root.
   256     ///\note The root node is reported to be reached!
   257     ///
   258     ///\pre \ref run() must be called before using this function.
   259     ///
   260     bool reached(Node v) { return v==source || (*predecessor)[v]!=INVALID; }
   261     
   262   };
   263   
   264 /// @}
   265   
   266 } //END OF NAMESPACE HUGO
   267 
   268 #endif
   269 
   270