lemon/bfs.h
author Balazs Dezso <deba@inf.elte.hu>
Fri, 13 Feb 2009 13:29:28 +0100
changeset 512 9b9ffe7d9b75
parent 420 6a2a33ad261b
child 492 9605e051942f
permissions -rw-r--r--
Fixes for MSVC 2008 in grap_adaptors.h and edge_set.h (#194)

Several renamings and changes in adaptors and edge sets

- Fixing scope usage for MSVC
- ResidualDigraph based on SubDigraph instead of FilterArcs
- Use initialize() in adaptors and edge sets
- Wrap ListDigraph for edge set tests
     1 /* -*- mode: C++; indent-tabs-mode: nil; -*-
     2  *
     3  * This file is a part of LEMON, a generic C++ optimization library.
     4  *
     5  * Copyright (C) 2003-2009
     6  * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
     7  * (Egervary Research Group on Combinatorial Optimization, EGRES).
     8  *
     9  * Permission to use, modify and distribute this software is granted
    10  * provided that this copyright notice appears in all copies. For
    11  * precise terms see the accompanying LICENSE file.
    12  *
    13  * This software is provided "AS IS" with no warranty of any kind,
    14  * express or implied, and with no claim as to its suitability for any
    15  * purpose.
    16  *
    17  */
    18 
    19 #ifndef LEMON_BFS_H
    20 #define LEMON_BFS_H
    21 
    22 ///\ingroup search
    23 ///\file
    24 ///\brief BFS algorithm.
    25 
    26 #include <lemon/list_graph.h>
    27 #include <lemon/bits/path_dump.h>
    28 #include <lemon/core.h>
    29 #include <lemon/error.h>
    30 #include <lemon/maps.h>
    31 #include <lemon/path.h>
    32 
    33 namespace lemon {
    34 
    35   ///Default traits class of Bfs class.
    36 
    37   ///Default traits class of Bfs class.
    38   ///\tparam GR Digraph type.
    39   template<class GR>
    40   struct BfsDefaultTraits
    41   {
    42     ///The type of the digraph the algorithm runs on.
    43     typedef GR Digraph;
    44 
    45     ///\brief The type of the map that stores the predecessor
    46     ///arcs of the shortest paths.
    47     ///
    48     ///The type of the map that stores the predecessor
    49     ///arcs of the shortest paths.
    50     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
    51     typedef typename Digraph::template NodeMap<typename Digraph::Arc> PredMap;
    52     ///Instantiates a PredMap.
    53 
    54     ///This function instantiates a PredMap.
    55     ///\param g is the digraph, to which we would like to define the
    56     ///PredMap.
    57     static PredMap *createPredMap(const Digraph &g)
    58     {
    59       return new PredMap(g);
    60     }
    61 
    62     ///The type of the map that indicates which nodes are processed.
    63 
    64     ///The type of the map that indicates which nodes are processed.
    65     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
    66     typedef NullMap<typename Digraph::Node,bool> ProcessedMap;
    67     ///Instantiates a ProcessedMap.
    68 
    69     ///This function instantiates a ProcessedMap.
    70     ///\param g is the digraph, to which
    71     ///we would like to define the ProcessedMap
    72 #ifdef DOXYGEN
    73     static ProcessedMap *createProcessedMap(const Digraph &g)
    74 #else
    75     static ProcessedMap *createProcessedMap(const Digraph &)
    76 #endif
    77     {
    78       return new ProcessedMap();
    79     }
    80 
    81     ///The type of the map that indicates which nodes are reached.
    82 
    83     ///The type of the map that indicates which nodes are reached.
    84     ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
    85     typedef typename Digraph::template NodeMap<bool> ReachedMap;
    86     ///Instantiates a ReachedMap.
    87 
    88     ///This function instantiates a ReachedMap.
    89     ///\param g is the digraph, to which
    90     ///we would like to define the ReachedMap.
    91     static ReachedMap *createReachedMap(const Digraph &g)
    92     {
    93       return new ReachedMap(g);
    94     }
    95 
    96     ///The type of the map that stores the distances of the nodes.
    97 
    98     ///The type of the map that stores the distances of the nodes.
    99     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   100     typedef typename Digraph::template NodeMap<int> DistMap;
   101     ///Instantiates a DistMap.
   102 
   103     ///This function instantiates a DistMap.
   104     ///\param g is the digraph, to which we would like to define the
   105     ///DistMap.
   106     static DistMap *createDistMap(const Digraph &g)
   107     {
   108       return new DistMap(g);
   109     }
   110   };
   111 
   112   ///%BFS algorithm class.
   113 
   114   ///\ingroup search
   115   ///This class provides an efficient implementation of the %BFS algorithm.
   116   ///
   117   ///There is also a \ref bfs() "function-type interface" for the BFS
   118   ///algorithm, which is convenient in the simplier cases and it can be
   119   ///used easier.
   120   ///
   121   ///\tparam GR The type of the digraph the algorithm runs on.
   122   ///The default type is \ref ListDigraph.
   123 #ifdef DOXYGEN
   124   template <typename GR,
   125             typename TR>
   126 #else
   127   template <typename GR=ListDigraph,
   128             typename TR=BfsDefaultTraits<GR> >
   129 #endif
   130   class Bfs {
   131   public:
   132 
   133     ///The type of the digraph the algorithm runs on.
   134     typedef typename TR::Digraph Digraph;
   135 
   136     ///\brief The type of the map that stores the predecessor arcs of the
   137     ///shortest paths.
   138     typedef typename TR::PredMap PredMap;
   139     ///The type of the map that stores the distances of the nodes.
   140     typedef typename TR::DistMap DistMap;
   141     ///The type of the map that indicates which nodes are reached.
   142     typedef typename TR::ReachedMap ReachedMap;
   143     ///The type of the map that indicates which nodes are processed.
   144     typedef typename TR::ProcessedMap ProcessedMap;
   145     ///The type of the paths.
   146     typedef PredMapPath<Digraph, PredMap> Path;
   147 
   148     ///The \ref BfsDefaultTraits "traits class" of the algorithm.
   149     typedef TR Traits;
   150 
   151   private:
   152 
   153     typedef typename Digraph::Node Node;
   154     typedef typename Digraph::NodeIt NodeIt;
   155     typedef typename Digraph::Arc Arc;
   156     typedef typename Digraph::OutArcIt OutArcIt;
   157 
   158     //Pointer to the underlying digraph.
   159     const Digraph *G;
   160     //Pointer to the map of predecessor arcs.
   161     PredMap *_pred;
   162     //Indicates if _pred is locally allocated (true) or not.
   163     bool local_pred;
   164     //Pointer to the map of distances.
   165     DistMap *_dist;
   166     //Indicates if _dist is locally allocated (true) or not.
   167     bool local_dist;
   168     //Pointer to the map of reached status of the nodes.
   169     ReachedMap *_reached;
   170     //Indicates if _reached is locally allocated (true) or not.
   171     bool local_reached;
   172     //Pointer to the map of processed status of the nodes.
   173     ProcessedMap *_processed;
   174     //Indicates if _processed is locally allocated (true) or not.
   175     bool local_processed;
   176 
   177     std::vector<typename Digraph::Node> _queue;
   178     int _queue_head,_queue_tail,_queue_next_dist;
   179     int _curr_dist;
   180 
   181     //Creates the maps if necessary.
   182     void create_maps()
   183     {
   184       if(!_pred) {
   185         local_pred = true;
   186         _pred = Traits::createPredMap(*G);
   187       }
   188       if(!_dist) {
   189         local_dist = true;
   190         _dist = Traits::createDistMap(*G);
   191       }
   192       if(!_reached) {
   193         local_reached = true;
   194         _reached = Traits::createReachedMap(*G);
   195       }
   196       if(!_processed) {
   197         local_processed = true;
   198         _processed = Traits::createProcessedMap(*G);
   199       }
   200     }
   201 
   202   protected:
   203 
   204     Bfs() {}
   205 
   206   public:
   207 
   208     typedef Bfs Create;
   209 
   210     ///\name Named Template Parameters
   211 
   212     ///@{
   213 
   214     template <class T>
   215     struct SetPredMapTraits : public Traits {
   216       typedef T PredMap;
   217       static PredMap *createPredMap(const Digraph &)
   218       {
   219         LEMON_ASSERT(false, "PredMap is not initialized");
   220         return 0; // ignore warnings
   221       }
   222     };
   223     ///\brief \ref named-templ-param "Named parameter" for setting
   224     ///PredMap type.
   225     ///
   226     ///\ref named-templ-param "Named parameter" for setting
   227     ///PredMap type.
   228     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   229     template <class T>
   230     struct SetPredMap : public Bfs< Digraph, SetPredMapTraits<T> > {
   231       typedef Bfs< Digraph, SetPredMapTraits<T> > Create;
   232     };
   233 
   234     template <class T>
   235     struct SetDistMapTraits : public Traits {
   236       typedef T DistMap;
   237       static DistMap *createDistMap(const Digraph &)
   238       {
   239         LEMON_ASSERT(false, "DistMap is not initialized");
   240         return 0; // ignore warnings
   241       }
   242     };
   243     ///\brief \ref named-templ-param "Named parameter" for setting
   244     ///DistMap type.
   245     ///
   246     ///\ref named-templ-param "Named parameter" for setting
   247     ///DistMap type.
   248     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   249     template <class T>
   250     struct SetDistMap : public Bfs< Digraph, SetDistMapTraits<T> > {
   251       typedef Bfs< Digraph, SetDistMapTraits<T> > Create;
   252     };
   253 
   254     template <class T>
   255     struct SetReachedMapTraits : public Traits {
   256       typedef T ReachedMap;
   257       static ReachedMap *createReachedMap(const Digraph &)
   258       {
   259         LEMON_ASSERT(false, "ReachedMap is not initialized");
   260         return 0; // ignore warnings
   261       }
   262     };
   263     ///\brief \ref named-templ-param "Named parameter" for setting
   264     ///ReachedMap type.
   265     ///
   266     ///\ref named-templ-param "Named parameter" for setting
   267     ///ReachedMap type.
   268     ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
   269     template <class T>
   270     struct SetReachedMap : public Bfs< Digraph, SetReachedMapTraits<T> > {
   271       typedef Bfs< Digraph, SetReachedMapTraits<T> > Create;
   272     };
   273 
   274     template <class T>
   275     struct SetProcessedMapTraits : public Traits {
   276       typedef T ProcessedMap;
   277       static ProcessedMap *createProcessedMap(const Digraph &)
   278       {
   279         LEMON_ASSERT(false, "ProcessedMap is not initialized");
   280         return 0; // ignore warnings
   281       }
   282     };
   283     ///\brief \ref named-templ-param "Named parameter" for setting
   284     ///ProcessedMap type.
   285     ///
   286     ///\ref named-templ-param "Named parameter" for setting
   287     ///ProcessedMap type.
   288     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   289     template <class T>
   290     struct SetProcessedMap : public Bfs< Digraph, SetProcessedMapTraits<T> > {
   291       typedef Bfs< Digraph, SetProcessedMapTraits<T> > Create;
   292     };
   293 
   294     struct SetStandardProcessedMapTraits : public Traits {
   295       typedef typename Digraph::template NodeMap<bool> ProcessedMap;
   296       static ProcessedMap *createProcessedMap(const Digraph &g)
   297       {
   298         return new ProcessedMap(g);
   299         return 0; // ignore warnings
   300       }
   301     };
   302     ///\brief \ref named-templ-param "Named parameter" for setting
   303     ///ProcessedMap type to be <tt>Digraph::NodeMap<bool></tt>.
   304     ///
   305     ///\ref named-templ-param "Named parameter" for setting
   306     ///ProcessedMap type to be <tt>Digraph::NodeMap<bool></tt>.
   307     ///If you don't set it explicitly, it will be automatically allocated.
   308     struct SetStandardProcessedMap :
   309       public Bfs< Digraph, SetStandardProcessedMapTraits > {
   310       typedef Bfs< Digraph, SetStandardProcessedMapTraits > Create;
   311     };
   312 
   313     ///@}
   314 
   315   public:
   316 
   317     ///Constructor.
   318 
   319     ///Constructor.
   320     ///\param g The digraph the algorithm runs on.
   321     Bfs(const Digraph &g) :
   322       G(&g),
   323       _pred(NULL), local_pred(false),
   324       _dist(NULL), local_dist(false),
   325       _reached(NULL), local_reached(false),
   326       _processed(NULL), local_processed(false)
   327     { }
   328 
   329     ///Destructor.
   330     ~Bfs()
   331     {
   332       if(local_pred) delete _pred;
   333       if(local_dist) delete _dist;
   334       if(local_reached) delete _reached;
   335       if(local_processed) delete _processed;
   336     }
   337 
   338     ///Sets the map that stores the predecessor arcs.
   339 
   340     ///Sets the map that stores the predecessor arcs.
   341     ///If you don't use this function before calling \ref run(Node) "run()"
   342     ///or \ref init(), an instance will be allocated automatically.
   343     ///The destructor deallocates this automatically allocated map,
   344     ///of course.
   345     ///\return <tt> (*this) </tt>
   346     Bfs &predMap(PredMap &m)
   347     {
   348       if(local_pred) {
   349         delete _pred;
   350         local_pred=false;
   351       }
   352       _pred = &m;
   353       return *this;
   354     }
   355 
   356     ///Sets the map that indicates which nodes are reached.
   357 
   358     ///Sets the map that indicates which nodes are reached.
   359     ///If you don't use this function before calling \ref run(Node) "run()"
   360     ///or \ref init(), an instance will be allocated automatically.
   361     ///The destructor deallocates this automatically allocated map,
   362     ///of course.
   363     ///\return <tt> (*this) </tt>
   364     Bfs &reachedMap(ReachedMap &m)
   365     {
   366       if(local_reached) {
   367         delete _reached;
   368         local_reached=false;
   369       }
   370       _reached = &m;
   371       return *this;
   372     }
   373 
   374     ///Sets the map that indicates which nodes are processed.
   375 
   376     ///Sets the map that indicates which nodes are processed.
   377     ///If you don't use this function before calling \ref run(Node) "run()"
   378     ///or \ref init(), an instance will be allocated automatically.
   379     ///The destructor deallocates this automatically allocated map,
   380     ///of course.
   381     ///\return <tt> (*this) </tt>
   382     Bfs &processedMap(ProcessedMap &m)
   383     {
   384       if(local_processed) {
   385         delete _processed;
   386         local_processed=false;
   387       }
   388       _processed = &m;
   389       return *this;
   390     }
   391 
   392     ///Sets the map that stores the distances of the nodes.
   393 
   394     ///Sets the map that stores the distances of the nodes calculated by
   395     ///the algorithm.
   396     ///If you don't use this function before calling \ref run(Node) "run()"
   397     ///or \ref init(), an instance will be allocated automatically.
   398     ///The destructor deallocates this automatically allocated map,
   399     ///of course.
   400     ///\return <tt> (*this) </tt>
   401     Bfs &distMap(DistMap &m)
   402     {
   403       if(local_dist) {
   404         delete _dist;
   405         local_dist=false;
   406       }
   407       _dist = &m;
   408       return *this;
   409     }
   410 
   411   public:
   412 
   413     ///\name Execution Control
   414     ///The simplest way to execute the BFS algorithm is to use one of the
   415     ///member functions called \ref run(Node) "run()".\n
   416     ///If you need more control on the execution, first you have to call
   417     ///\ref init(), then you can add several source nodes with
   418     ///\ref addSource(). Finally the actual path computation can be
   419     ///performed with one of the \ref start() functions.
   420 
   421     ///@{
   422 
   423     ///\brief Initializes the internal data structures.
   424     ///
   425     ///Initializes the internal data structures.
   426     void init()
   427     {
   428       create_maps();
   429       _queue.resize(countNodes(*G));
   430       _queue_head=_queue_tail=0;
   431       _curr_dist=1;
   432       for ( NodeIt u(*G) ; u!=INVALID ; ++u ) {
   433         _pred->set(u,INVALID);
   434         _reached->set(u,false);
   435         _processed->set(u,false);
   436       }
   437     }
   438 
   439     ///Adds a new source node.
   440 
   441     ///Adds a new source node to the set of nodes to be processed.
   442     ///
   443     void addSource(Node s)
   444     {
   445       if(!(*_reached)[s])
   446         {
   447           _reached->set(s,true);
   448           _pred->set(s,INVALID);
   449           _dist->set(s,0);
   450           _queue[_queue_head++]=s;
   451           _queue_next_dist=_queue_head;
   452         }
   453     }
   454 
   455     ///Processes the next node.
   456 
   457     ///Processes the next node.
   458     ///
   459     ///\return The processed node.
   460     ///
   461     ///\pre The queue must not be empty.
   462     Node processNextNode()
   463     {
   464       if(_queue_tail==_queue_next_dist) {
   465         _curr_dist++;
   466         _queue_next_dist=_queue_head;
   467       }
   468       Node n=_queue[_queue_tail++];
   469       _processed->set(n,true);
   470       Node m;
   471       for(OutArcIt e(*G,n);e!=INVALID;++e)
   472         if(!(*_reached)[m=G->target(e)]) {
   473           _queue[_queue_head++]=m;
   474           _reached->set(m,true);
   475           _pred->set(m,e);
   476           _dist->set(m,_curr_dist);
   477         }
   478       return n;
   479     }
   480 
   481     ///Processes the next node.
   482 
   483     ///Processes the next node and checks if the given target node
   484     ///is reached. If the target node is reachable from the processed
   485     ///node, then the \c reach parameter will be set to \c true.
   486     ///
   487     ///\param target The target node.
   488     ///\retval reach Indicates if the target node is reached.
   489     ///It should be initially \c false.
   490     ///
   491     ///\return The processed node.
   492     ///
   493     ///\pre The queue must not be empty.
   494     Node processNextNode(Node target, bool& reach)
   495     {
   496       if(_queue_tail==_queue_next_dist) {
   497         _curr_dist++;
   498         _queue_next_dist=_queue_head;
   499       }
   500       Node n=_queue[_queue_tail++];
   501       _processed->set(n,true);
   502       Node m;
   503       for(OutArcIt e(*G,n);e!=INVALID;++e)
   504         if(!(*_reached)[m=G->target(e)]) {
   505           _queue[_queue_head++]=m;
   506           _reached->set(m,true);
   507           _pred->set(m,e);
   508           _dist->set(m,_curr_dist);
   509           reach = reach || (target == m);
   510         }
   511       return n;
   512     }
   513 
   514     ///Processes the next node.
   515 
   516     ///Processes the next node and checks if at least one of reached
   517     ///nodes has \c true value in the \c nm node map. If one node
   518     ///with \c true value is reachable from the processed node, then the
   519     ///\c rnode parameter will be set to the first of such nodes.
   520     ///
   521     ///\param nm A \c bool (or convertible) node map that indicates the
   522     ///possible targets.
   523     ///\retval rnode The reached target node.
   524     ///It should be initially \c INVALID.
   525     ///
   526     ///\return The processed node.
   527     ///
   528     ///\pre The queue must not be empty.
   529     template<class NM>
   530     Node processNextNode(const NM& nm, Node& rnode)
   531     {
   532       if(_queue_tail==_queue_next_dist) {
   533         _curr_dist++;
   534         _queue_next_dist=_queue_head;
   535       }
   536       Node n=_queue[_queue_tail++];
   537       _processed->set(n,true);
   538       Node m;
   539       for(OutArcIt e(*G,n);e!=INVALID;++e)
   540         if(!(*_reached)[m=G->target(e)]) {
   541           _queue[_queue_head++]=m;
   542           _reached->set(m,true);
   543           _pred->set(m,e);
   544           _dist->set(m,_curr_dist);
   545           if (nm[m] && rnode == INVALID) rnode = m;
   546         }
   547       return n;
   548     }
   549 
   550     ///The next node to be processed.
   551 
   552     ///Returns the next node to be processed or \c INVALID if the queue
   553     ///is empty.
   554     Node nextNode() const
   555     {
   556       return _queue_tail<_queue_head?_queue[_queue_tail]:INVALID;
   557     }
   558 
   559     ///Returns \c false if there are nodes to be processed.
   560 
   561     ///Returns \c false if there are nodes to be processed
   562     ///in the queue.
   563     bool emptyQueue() const { return _queue_tail==_queue_head; }
   564 
   565     ///Returns the number of the nodes to be processed.
   566 
   567     ///Returns the number of the nodes to be processed
   568     ///in the queue.
   569     int queueSize() const { return _queue_head-_queue_tail; }
   570 
   571     ///Executes the algorithm.
   572 
   573     ///Executes the algorithm.
   574     ///
   575     ///This method runs the %BFS algorithm from the root node(s)
   576     ///in order to compute the shortest path to each node.
   577     ///
   578     ///The algorithm computes
   579     ///- the shortest path tree (forest),
   580     ///- the distance of each node from the root(s).
   581     ///
   582     ///\pre init() must be called and at least one root node should be
   583     ///added with addSource() before using this function.
   584     ///
   585     ///\note <tt>b.start()</tt> is just a shortcut of the following code.
   586     ///\code
   587     ///  while ( !b.emptyQueue() ) {
   588     ///    b.processNextNode();
   589     ///  }
   590     ///\endcode
   591     void start()
   592     {
   593       while ( !emptyQueue() ) processNextNode();
   594     }
   595 
   596     ///Executes the algorithm until the given target node is reached.
   597 
   598     ///Executes the algorithm until the given target node is reached.
   599     ///
   600     ///This method runs the %BFS algorithm from the root node(s)
   601     ///in order to compute the shortest path to \c t.
   602     ///
   603     ///The algorithm computes
   604     ///- the shortest path to \c t,
   605     ///- the distance of \c t from the root(s).
   606     ///
   607     ///\pre init() must be called and at least one root node should be
   608     ///added with addSource() before using this function.
   609     ///
   610     ///\note <tt>b.start(t)</tt> is just a shortcut of the following code.
   611     ///\code
   612     ///  bool reach = false;
   613     ///  while ( !b.emptyQueue() && !reach ) {
   614     ///    b.processNextNode(t, reach);
   615     ///  }
   616     ///\endcode
   617     void start(Node t)
   618     {
   619       bool reach = false;
   620       while ( !emptyQueue() && !reach ) processNextNode(t, reach);
   621     }
   622 
   623     ///Executes the algorithm until a condition is met.
   624 
   625     ///Executes the algorithm until a condition is met.
   626     ///
   627     ///This method runs the %BFS algorithm from the root node(s) in
   628     ///order to compute the shortest path to a node \c v with
   629     /// <tt>nm[v]</tt> true, if such a node can be found.
   630     ///
   631     ///\param nm A \c bool (or convertible) node map. The algorithm
   632     ///will stop when it reaches a node \c v with <tt>nm[v]</tt> true.
   633     ///
   634     ///\return The reached node \c v with <tt>nm[v]</tt> true or
   635     ///\c INVALID if no such node was found.
   636     ///
   637     ///\pre init() must be called and at least one root node should be
   638     ///added with addSource() before using this function.
   639     ///
   640     ///\note <tt>b.start(nm)</tt> is just a shortcut of the following code.
   641     ///\code
   642     ///  Node rnode = INVALID;
   643     ///  while ( !b.emptyQueue() && rnode == INVALID ) {
   644     ///    b.processNextNode(nm, rnode);
   645     ///  }
   646     ///  return rnode;
   647     ///\endcode
   648     template<class NodeBoolMap>
   649     Node start(const NodeBoolMap &nm)
   650     {
   651       Node rnode = INVALID;
   652       while ( !emptyQueue() && rnode == INVALID ) {
   653         processNextNode(nm, rnode);
   654       }
   655       return rnode;
   656     }
   657 
   658     ///Runs the algorithm from the given source node.
   659 
   660     ///This method runs the %BFS algorithm from node \c s
   661     ///in order to compute the shortest path to each node.
   662     ///
   663     ///The algorithm computes
   664     ///- the shortest path tree,
   665     ///- the distance of each node from the root.
   666     ///
   667     ///\note <tt>b.run(s)</tt> is just a shortcut of the following code.
   668     ///\code
   669     ///  b.init();
   670     ///  b.addSource(s);
   671     ///  b.start();
   672     ///\endcode
   673     void run(Node s) {
   674       init();
   675       addSource(s);
   676       start();
   677     }
   678 
   679     ///Finds the shortest path between \c s and \c t.
   680 
   681     ///This method runs the %BFS algorithm from node \c s
   682     ///in order to compute the shortest path to node \c t
   683     ///(it stops searching when \c t is processed).
   684     ///
   685     ///\return \c true if \c t is reachable form \c s.
   686     ///
   687     ///\note Apart from the return value, <tt>b.run(s,t)</tt> is just a
   688     ///shortcut of the following code.
   689     ///\code
   690     ///  b.init();
   691     ///  b.addSource(s);
   692     ///  b.start(t);
   693     ///\endcode
   694     bool run(Node s,Node t) {
   695       init();
   696       addSource(s);
   697       start(t);
   698       return reached(t);
   699     }
   700 
   701     ///Runs the algorithm to visit all nodes in the digraph.
   702 
   703     ///This method runs the %BFS algorithm in order to
   704     ///compute the shortest path to each node.
   705     ///
   706     ///The algorithm computes
   707     ///- the shortest path tree (forest),
   708     ///- the distance of each node from the root(s).
   709     ///
   710     ///\note <tt>b.run(s)</tt> is just a shortcut of the following code.
   711     ///\code
   712     ///  b.init();
   713     ///  for (NodeIt n(gr); n != INVALID; ++n) {
   714     ///    if (!b.reached(n)) {
   715     ///      b.addSource(n);
   716     ///      b.start();
   717     ///    }
   718     ///  }
   719     ///\endcode
   720     void run() {
   721       init();
   722       for (NodeIt n(*G); n != INVALID; ++n) {
   723         if (!reached(n)) {
   724           addSource(n);
   725           start();
   726         }
   727       }
   728     }
   729 
   730     ///@}
   731 
   732     ///\name Query Functions
   733     ///The results of the BFS algorithm can be obtained using these
   734     ///functions.\n
   735     ///Either \ref run(Node) "run()" or \ref start() should be called
   736     ///before using them.
   737 
   738     ///@{
   739 
   740     ///The shortest path to a node.
   741 
   742     ///Returns the shortest path to a node.
   743     ///
   744     ///\warning \c t should be reached from the root(s).
   745     ///
   746     ///\pre Either \ref run(Node) "run()" or \ref init()
   747     ///must be called before using this function.
   748     Path path(Node t) const { return Path(*G, *_pred, t); }
   749 
   750     ///The distance of a node from the root(s).
   751 
   752     ///Returns the distance of a node from the root(s).
   753     ///
   754     ///\warning If node \c v is not reached from the root(s), then
   755     ///the return value of this function is undefined.
   756     ///
   757     ///\pre Either \ref run(Node) "run()" or \ref init()
   758     ///must be called before using this function.
   759     int dist(Node v) const { return (*_dist)[v]; }
   760 
   761     ///Returns the 'previous arc' of the shortest path tree for a node.
   762 
   763     ///This function returns the 'previous arc' of the shortest path
   764     ///tree for the node \c v, i.e. it returns the last arc of a
   765     ///shortest path from a root to \c v. It is \c INVALID if \c v
   766     ///is not reached from the root(s) or if \c v is a root.
   767     ///
   768     ///The shortest path tree used here is equal to the shortest path
   769     ///tree used in \ref predNode().
   770     ///
   771     ///\pre Either \ref run(Node) "run()" or \ref init()
   772     ///must be called before using this function.
   773     Arc predArc(Node v) const { return (*_pred)[v];}
   774 
   775     ///Returns the 'previous node' of the shortest path tree for a node.
   776 
   777     ///This function returns the 'previous node' of the shortest path
   778     ///tree for the node \c v, i.e. it returns the last but one node
   779     ///from a shortest path from a root to \c v. It is \c INVALID
   780     ///if \c v is not reached from the root(s) or if \c v is a root.
   781     ///
   782     ///The shortest path tree used here is equal to the shortest path
   783     ///tree used in \ref predArc().
   784     ///
   785     ///\pre Either \ref run(Node) "run()" or \ref init()
   786     ///must be called before using this function.
   787     Node predNode(Node v) const { return (*_pred)[v]==INVALID ? INVALID:
   788                                   G->source((*_pred)[v]); }
   789 
   790     ///\brief Returns a const reference to the node map that stores the
   791     /// distances of the nodes.
   792     ///
   793     ///Returns a const reference to the node map that stores the distances
   794     ///of the nodes calculated by the algorithm.
   795     ///
   796     ///\pre Either \ref run(Node) "run()" or \ref init()
   797     ///must be called before using this function.
   798     const DistMap &distMap() const { return *_dist;}
   799 
   800     ///\brief Returns a const reference to the node map that stores the
   801     ///predecessor arcs.
   802     ///
   803     ///Returns a const reference to the node map that stores the predecessor
   804     ///arcs, which form the shortest path tree.
   805     ///
   806     ///\pre Either \ref run(Node) "run()" or \ref init()
   807     ///must be called before using this function.
   808     const PredMap &predMap() const { return *_pred;}
   809 
   810     ///Checks if a node is reached from the root(s).
   811 
   812     ///Returns \c true if \c v is reached from the root(s).
   813     ///
   814     ///\pre Either \ref run(Node) "run()" or \ref init()
   815     ///must be called before using this function.
   816     bool reached(Node v) const { return (*_reached)[v]; }
   817 
   818     ///@}
   819   };
   820 
   821   ///Default traits class of bfs() function.
   822 
   823   ///Default traits class of bfs() function.
   824   ///\tparam GR Digraph type.
   825   template<class GR>
   826   struct BfsWizardDefaultTraits
   827   {
   828     ///The type of the digraph the algorithm runs on.
   829     typedef GR Digraph;
   830 
   831     ///\brief The type of the map that stores the predecessor
   832     ///arcs of the shortest paths.
   833     ///
   834     ///The type of the map that stores the predecessor
   835     ///arcs of the shortest paths.
   836     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   837     typedef typename Digraph::template NodeMap<typename Digraph::Arc> PredMap;
   838     ///Instantiates a PredMap.
   839 
   840     ///This function instantiates a PredMap.
   841     ///\param g is the digraph, to which we would like to define the
   842     ///PredMap.
   843     static PredMap *createPredMap(const Digraph &g)
   844     {
   845       return new PredMap(g);
   846     }
   847 
   848     ///The type of the map that indicates which nodes are processed.
   849 
   850     ///The type of the map that indicates which nodes are processed.
   851     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   852     ///By default it is a NullMap.
   853     typedef NullMap<typename Digraph::Node,bool> ProcessedMap;
   854     ///Instantiates a ProcessedMap.
   855 
   856     ///This function instantiates a ProcessedMap.
   857     ///\param g is the digraph, to which
   858     ///we would like to define the ProcessedMap.
   859 #ifdef DOXYGEN
   860     static ProcessedMap *createProcessedMap(const Digraph &g)
   861 #else
   862     static ProcessedMap *createProcessedMap(const Digraph &)
   863 #endif
   864     {
   865       return new ProcessedMap();
   866     }
   867 
   868     ///The type of the map that indicates which nodes are reached.
   869 
   870     ///The type of the map that indicates which nodes are reached.
   871     ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
   872     typedef typename Digraph::template NodeMap<bool> ReachedMap;
   873     ///Instantiates a ReachedMap.
   874 
   875     ///This function instantiates a ReachedMap.
   876     ///\param g is the digraph, to which
   877     ///we would like to define the ReachedMap.
   878     static ReachedMap *createReachedMap(const Digraph &g)
   879     {
   880       return new ReachedMap(g);
   881     }
   882 
   883     ///The type of the map that stores the distances of the nodes.
   884 
   885     ///The type of the map that stores the distances of the nodes.
   886     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   887     typedef typename Digraph::template NodeMap<int> DistMap;
   888     ///Instantiates a DistMap.
   889 
   890     ///This function instantiates a DistMap.
   891     ///\param g is the digraph, to which we would like to define
   892     ///the DistMap
   893     static DistMap *createDistMap(const Digraph &g)
   894     {
   895       return new DistMap(g);
   896     }
   897 
   898     ///The type of the shortest paths.
   899 
   900     ///The type of the shortest paths.
   901     ///It must meet the \ref concepts::Path "Path" concept.
   902     typedef lemon::Path<Digraph> Path;
   903   };
   904 
   905   /// Default traits class used by BfsWizard
   906 
   907   /// To make it easier to use Bfs algorithm
   908   /// we have created a wizard class.
   909   /// This \ref BfsWizard class needs default traits,
   910   /// as well as the \ref Bfs class.
   911   /// The \ref BfsWizardBase is a class to be the default traits of the
   912   /// \ref BfsWizard class.
   913   template<class GR>
   914   class BfsWizardBase : public BfsWizardDefaultTraits<GR>
   915   {
   916 
   917     typedef BfsWizardDefaultTraits<GR> Base;
   918   protected:
   919     //The type of the nodes in the digraph.
   920     typedef typename Base::Digraph::Node Node;
   921 
   922     //Pointer to the digraph the algorithm runs on.
   923     void *_g;
   924     //Pointer to the map of reached nodes.
   925     void *_reached;
   926     //Pointer to the map of processed nodes.
   927     void *_processed;
   928     //Pointer to the map of predecessors arcs.
   929     void *_pred;
   930     //Pointer to the map of distances.
   931     void *_dist;
   932     //Pointer to the shortest path to the target node.
   933     void *_path;
   934     //Pointer to the distance of the target node.
   935     int *_di;
   936 
   937     public:
   938     /// Constructor.
   939 
   940     /// This constructor does not require parameters, therefore it initiates
   941     /// all of the attributes to \c 0.
   942     BfsWizardBase() : _g(0), _reached(0), _processed(0), _pred(0),
   943                       _dist(0), _path(0), _di(0) {}
   944 
   945     /// Constructor.
   946 
   947     /// This constructor requires one parameter,
   948     /// others are initiated to \c 0.
   949     /// \param g The digraph the algorithm runs on.
   950     BfsWizardBase(const GR &g) :
   951       _g(reinterpret_cast<void*>(const_cast<GR*>(&g))),
   952       _reached(0), _processed(0), _pred(0), _dist(0),  _path(0), _di(0) {}
   953 
   954   };
   955 
   956   /// Auxiliary class for the function-type interface of BFS algorithm.
   957 
   958   /// This auxiliary class is created to implement the
   959   /// \ref bfs() "function-type interface" of \ref Bfs algorithm.
   960   /// It does not have own \ref run(Node) "run()" method, it uses the
   961   /// functions and features of the plain \ref Bfs.
   962   ///
   963   /// This class should only be used through the \ref bfs() function,
   964   /// which makes it easier to use the algorithm.
   965   template<class TR>
   966   class BfsWizard : public TR
   967   {
   968     typedef TR Base;
   969 
   970     ///The type of the digraph the algorithm runs on.
   971     typedef typename TR::Digraph Digraph;
   972 
   973     typedef typename Digraph::Node Node;
   974     typedef typename Digraph::NodeIt NodeIt;
   975     typedef typename Digraph::Arc Arc;
   976     typedef typename Digraph::OutArcIt OutArcIt;
   977 
   978     ///\brief The type of the map that stores the predecessor
   979     ///arcs of the shortest paths.
   980     typedef typename TR::PredMap PredMap;
   981     ///\brief The type of the map that stores the distances of the nodes.
   982     typedef typename TR::DistMap DistMap;
   983     ///\brief The type of the map that indicates which nodes are reached.
   984     typedef typename TR::ReachedMap ReachedMap;
   985     ///\brief The type of the map that indicates which nodes are processed.
   986     typedef typename TR::ProcessedMap ProcessedMap;
   987     ///The type of the shortest paths
   988     typedef typename TR::Path Path;
   989 
   990   public:
   991 
   992     /// Constructor.
   993     BfsWizard() : TR() {}
   994 
   995     /// Constructor that requires parameters.
   996 
   997     /// Constructor that requires parameters.
   998     /// These parameters will be the default values for the traits class.
   999     /// \param g The digraph the algorithm runs on.
  1000     BfsWizard(const Digraph &g) :
  1001       TR(g) {}
  1002 
  1003     ///Copy constructor
  1004     BfsWizard(const TR &b) : TR(b) {}
  1005 
  1006     ~BfsWizard() {}
  1007 
  1008     ///Runs BFS algorithm from the given source node.
  1009 
  1010     ///This method runs BFS algorithm from node \c s
  1011     ///in order to compute the shortest path to each node.
  1012     void run(Node s)
  1013     {
  1014       Bfs<Digraph,TR> alg(*reinterpret_cast<const Digraph*>(Base::_g));
  1015       if (Base::_pred)
  1016         alg.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
  1017       if (Base::_dist)
  1018         alg.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
  1019       if (Base::_reached)
  1020         alg.reachedMap(*reinterpret_cast<ReachedMap*>(Base::_reached));
  1021       if (Base::_processed)
  1022         alg.processedMap(*reinterpret_cast<ProcessedMap*>(Base::_processed));
  1023       if (s!=INVALID)
  1024         alg.run(s);
  1025       else
  1026         alg.run();
  1027     }
  1028 
  1029     ///Finds the shortest path between \c s and \c t.
  1030 
  1031     ///This method runs BFS algorithm from node \c s
  1032     ///in order to compute the shortest path to node \c t
  1033     ///(it stops searching when \c t is processed).
  1034     ///
  1035     ///\return \c true if \c t is reachable form \c s.
  1036     bool run(Node s, Node t)
  1037     {
  1038       Bfs<Digraph,TR> alg(*reinterpret_cast<const Digraph*>(Base::_g));
  1039       if (Base::_pred)
  1040         alg.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
  1041       if (Base::_dist)
  1042         alg.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
  1043       if (Base::_reached)
  1044         alg.reachedMap(*reinterpret_cast<ReachedMap*>(Base::_reached));
  1045       if (Base::_processed)
  1046         alg.processedMap(*reinterpret_cast<ProcessedMap*>(Base::_processed));
  1047       alg.run(s,t);
  1048       if (Base::_path)
  1049         *reinterpret_cast<Path*>(Base::_path) = alg.path(t);
  1050       if (Base::_di)
  1051         *Base::_di = alg.dist(t);
  1052       return alg.reached(t);
  1053     }
  1054 
  1055     ///Runs BFS algorithm to visit all nodes in the digraph.
  1056 
  1057     ///This method runs BFS algorithm in order to compute
  1058     ///the shortest path to each node.
  1059     void run()
  1060     {
  1061       run(INVALID);
  1062     }
  1063 
  1064     template<class T>
  1065     struct SetPredMapBase : public Base {
  1066       typedef T PredMap;
  1067       static PredMap *createPredMap(const Digraph &) { return 0; };
  1068       SetPredMapBase(const TR &b) : TR(b) {}
  1069     };
  1070     ///\brief \ref named-func-param "Named parameter"
  1071     ///for setting PredMap object.
  1072     ///
  1073     ///\ref named-func-param "Named parameter"
  1074     ///for setting PredMap object.
  1075     template<class T>
  1076     BfsWizard<SetPredMapBase<T> > predMap(const T &t)
  1077     {
  1078       Base::_pred=reinterpret_cast<void*>(const_cast<T*>(&t));
  1079       return BfsWizard<SetPredMapBase<T> >(*this);
  1080     }
  1081 
  1082     template<class T>
  1083     struct SetReachedMapBase : public Base {
  1084       typedef T ReachedMap;
  1085       static ReachedMap *createReachedMap(const Digraph &) { return 0; };
  1086       SetReachedMapBase(const TR &b) : TR(b) {}
  1087     };
  1088     ///\brief \ref named-func-param "Named parameter"
  1089     ///for setting ReachedMap object.
  1090     ///
  1091     /// \ref named-func-param "Named parameter"
  1092     ///for setting ReachedMap object.
  1093     template<class T>
  1094     BfsWizard<SetReachedMapBase<T> > reachedMap(const T &t)
  1095     {
  1096       Base::_reached=reinterpret_cast<void*>(const_cast<T*>(&t));
  1097       return BfsWizard<SetReachedMapBase<T> >(*this);
  1098     }
  1099 
  1100     template<class T>
  1101     struct SetDistMapBase : public Base {
  1102       typedef T DistMap;
  1103       static DistMap *createDistMap(const Digraph &) { return 0; };
  1104       SetDistMapBase(const TR &b) : TR(b) {}
  1105     };
  1106     ///\brief \ref named-func-param "Named parameter"
  1107     ///for setting DistMap object.
  1108     ///
  1109     /// \ref named-func-param "Named parameter"
  1110     ///for setting DistMap object.
  1111     template<class T>
  1112     BfsWizard<SetDistMapBase<T> > distMap(const T &t)
  1113     {
  1114       Base::_dist=reinterpret_cast<void*>(const_cast<T*>(&t));
  1115       return BfsWizard<SetDistMapBase<T> >(*this);
  1116     }
  1117 
  1118     template<class T>
  1119     struct SetProcessedMapBase : public Base {
  1120       typedef T ProcessedMap;
  1121       static ProcessedMap *createProcessedMap(const Digraph &) { return 0; };
  1122       SetProcessedMapBase(const TR &b) : TR(b) {}
  1123     };
  1124     ///\brief \ref named-func-param "Named parameter"
  1125     ///for setting ProcessedMap object.
  1126     ///
  1127     /// \ref named-func-param "Named parameter"
  1128     ///for setting ProcessedMap object.
  1129     template<class T>
  1130     BfsWizard<SetProcessedMapBase<T> > processedMap(const T &t)
  1131     {
  1132       Base::_processed=reinterpret_cast<void*>(const_cast<T*>(&t));
  1133       return BfsWizard<SetProcessedMapBase<T> >(*this);
  1134     }
  1135 
  1136     template<class T>
  1137     struct SetPathBase : public Base {
  1138       typedef T Path;
  1139       SetPathBase(const TR &b) : TR(b) {}
  1140     };
  1141     ///\brief \ref named-func-param "Named parameter"
  1142     ///for getting the shortest path to the target node.
  1143     ///
  1144     ///\ref named-func-param "Named parameter"
  1145     ///for getting the shortest path to the target node.
  1146     template<class T>
  1147     BfsWizard<SetPathBase<T> > path(const T &t)
  1148     {
  1149       Base::_path=reinterpret_cast<void*>(const_cast<T*>(&t));
  1150       return BfsWizard<SetPathBase<T> >(*this);
  1151     }
  1152 
  1153     ///\brief \ref named-func-param "Named parameter"
  1154     ///for getting the distance of the target node.
  1155     ///
  1156     ///\ref named-func-param "Named parameter"
  1157     ///for getting the distance of the target node.
  1158     BfsWizard dist(const int &d)
  1159     {
  1160       Base::_di=const_cast<int*>(&d);
  1161       return *this;
  1162     }
  1163 
  1164   };
  1165 
  1166   ///Function-type interface for BFS algorithm.
  1167 
  1168   /// \ingroup search
  1169   ///Function-type interface for BFS algorithm.
  1170   ///
  1171   ///This function also has several \ref named-func-param "named parameters",
  1172   ///they are declared as the members of class \ref BfsWizard.
  1173   ///The following examples show how to use these parameters.
  1174   ///\code
  1175   ///  // Compute shortest path from node s to each node
  1176   ///  bfs(g).predMap(preds).distMap(dists).run(s);
  1177   ///
  1178   ///  // Compute shortest path from s to t
  1179   ///  bool reached = bfs(g).path(p).dist(d).run(s,t);
  1180   ///\endcode
  1181   ///\warning Don't forget to put the \ref BfsWizard::run(Node) "run()"
  1182   ///to the end of the parameter list.
  1183   ///\sa BfsWizard
  1184   ///\sa Bfs
  1185   template<class GR>
  1186   BfsWizard<BfsWizardBase<GR> >
  1187   bfs(const GR &digraph)
  1188   {
  1189     return BfsWizard<BfsWizardBase<GR> >(digraph);
  1190   }
  1191 
  1192 #ifdef DOXYGEN
  1193   /// \brief Visitor class for BFS.
  1194   ///
  1195   /// This class defines the interface of the BfsVisit events, and
  1196   /// it could be the base of a real visitor class.
  1197   template <typename _Digraph>
  1198   struct BfsVisitor {
  1199     typedef _Digraph Digraph;
  1200     typedef typename Digraph::Arc Arc;
  1201     typedef typename Digraph::Node Node;
  1202     /// \brief Called for the source node(s) of the BFS.
  1203     ///
  1204     /// This function is called for the source node(s) of the BFS.
  1205     void start(const Node& node) {}
  1206     /// \brief Called when a node is reached first time.
  1207     ///
  1208     /// This function is called when a node is reached first time.
  1209     void reach(const Node& node) {}
  1210     /// \brief Called when a node is processed.
  1211     ///
  1212     /// This function is called when a node is processed.
  1213     void process(const Node& node) {}
  1214     /// \brief Called when an arc reaches a new node.
  1215     ///
  1216     /// This function is called when the BFS finds an arc whose target node
  1217     /// is not reached yet.
  1218     void discover(const Arc& arc) {}
  1219     /// \brief Called when an arc is examined but its target node is
  1220     /// already discovered.
  1221     ///
  1222     /// This function is called when an arc is examined but its target node is
  1223     /// already discovered.
  1224     void examine(const Arc& arc) {}
  1225   };
  1226 #else
  1227   template <typename _Digraph>
  1228   struct BfsVisitor {
  1229     typedef _Digraph Digraph;
  1230     typedef typename Digraph::Arc Arc;
  1231     typedef typename Digraph::Node Node;
  1232     void start(const Node&) {}
  1233     void reach(const Node&) {}
  1234     void process(const Node&) {}
  1235     void discover(const Arc&) {}
  1236     void examine(const Arc&) {}
  1237 
  1238     template <typename _Visitor>
  1239     struct Constraints {
  1240       void constraints() {
  1241         Arc arc;
  1242         Node node;
  1243         visitor.start(node);
  1244         visitor.reach(node);
  1245         visitor.process(node);
  1246         visitor.discover(arc);
  1247         visitor.examine(arc);
  1248       }
  1249       _Visitor& visitor;
  1250     };
  1251   };
  1252 #endif
  1253 
  1254   /// \brief Default traits class of BfsVisit class.
  1255   ///
  1256   /// Default traits class of BfsVisit class.
  1257   /// \tparam _Digraph The type of the digraph the algorithm runs on.
  1258   template<class _Digraph>
  1259   struct BfsVisitDefaultTraits {
  1260 
  1261     /// \brief The type of the digraph the algorithm runs on.
  1262     typedef _Digraph Digraph;
  1263 
  1264     /// \brief The type of the map that indicates which nodes are reached.
  1265     ///
  1266     /// The type of the map that indicates which nodes are reached.
  1267     /// It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
  1268     typedef typename Digraph::template NodeMap<bool> ReachedMap;
  1269 
  1270     /// \brief Instantiates a ReachedMap.
  1271     ///
  1272     /// This function instantiates a ReachedMap.
  1273     /// \param digraph is the digraph, to which
  1274     /// we would like to define the ReachedMap.
  1275     static ReachedMap *createReachedMap(const Digraph &digraph) {
  1276       return new ReachedMap(digraph);
  1277     }
  1278 
  1279   };
  1280 
  1281   /// \ingroup search
  1282   ///
  1283   /// \brief %BFS algorithm class with visitor interface.
  1284   ///
  1285   /// This class provides an efficient implementation of the %BFS algorithm
  1286   /// with visitor interface.
  1287   ///
  1288   /// The %BfsVisit class provides an alternative interface to the Bfs
  1289   /// class. It works with callback mechanism, the BfsVisit object calls
  1290   /// the member functions of the \c Visitor class on every BFS event.
  1291   ///
  1292   /// This interface of the BFS algorithm should be used in special cases
  1293   /// when extra actions have to be performed in connection with certain
  1294   /// events of the BFS algorithm. Otherwise consider to use Bfs or bfs()
  1295   /// instead.
  1296   ///
  1297   /// \tparam _Digraph The type of the digraph the algorithm runs on.
  1298   /// The default value is
  1299   /// \ref ListDigraph. The value of _Digraph is not used directly by
  1300   /// \ref BfsVisit, it is only passed to \ref BfsVisitDefaultTraits.
  1301   /// \tparam _Visitor The Visitor type that is used by the algorithm.
  1302   /// \ref BfsVisitor "BfsVisitor<_Digraph>" is an empty visitor, which
  1303   /// does not observe the BFS events. If you want to observe the BFS
  1304   /// events, you should implement your own visitor class.
  1305   /// \tparam _Traits Traits class to set various data types used by the
  1306   /// algorithm. The default traits class is
  1307   /// \ref BfsVisitDefaultTraits "BfsVisitDefaultTraits<_Digraph>".
  1308   /// See \ref BfsVisitDefaultTraits for the documentation of
  1309   /// a BFS visit traits class.
  1310 #ifdef DOXYGEN
  1311   template <typename _Digraph, typename _Visitor, typename _Traits>
  1312 #else
  1313   template <typename _Digraph = ListDigraph,
  1314             typename _Visitor = BfsVisitor<_Digraph>,
  1315             typename _Traits = BfsVisitDefaultTraits<_Digraph> >
  1316 #endif
  1317   class BfsVisit {
  1318   public:
  1319 
  1320     ///The traits class.
  1321     typedef _Traits Traits;
  1322 
  1323     ///The type of the digraph the algorithm runs on.
  1324     typedef typename Traits::Digraph Digraph;
  1325 
  1326     ///The visitor type used by the algorithm.
  1327     typedef _Visitor Visitor;
  1328 
  1329     ///The type of the map that indicates which nodes are reached.
  1330     typedef typename Traits::ReachedMap ReachedMap;
  1331 
  1332   private:
  1333 
  1334     typedef typename Digraph::Node Node;
  1335     typedef typename Digraph::NodeIt NodeIt;
  1336     typedef typename Digraph::Arc Arc;
  1337     typedef typename Digraph::OutArcIt OutArcIt;
  1338 
  1339     //Pointer to the underlying digraph.
  1340     const Digraph *_digraph;
  1341     //Pointer to the visitor object.
  1342     Visitor *_visitor;
  1343     //Pointer to the map of reached status of the nodes.
  1344     ReachedMap *_reached;
  1345     //Indicates if _reached is locally allocated (true) or not.
  1346     bool local_reached;
  1347 
  1348     std::vector<typename Digraph::Node> _list;
  1349     int _list_front, _list_back;
  1350 
  1351     //Creates the maps if necessary.
  1352     void create_maps() {
  1353       if(!_reached) {
  1354         local_reached = true;
  1355         _reached = Traits::createReachedMap(*_digraph);
  1356       }
  1357     }
  1358 
  1359   protected:
  1360 
  1361     BfsVisit() {}
  1362 
  1363   public:
  1364 
  1365     typedef BfsVisit Create;
  1366 
  1367     /// \name Named Template Parameters
  1368 
  1369     ///@{
  1370     template <class T>
  1371     struct SetReachedMapTraits : public Traits {
  1372       typedef T ReachedMap;
  1373       static ReachedMap *createReachedMap(const Digraph &digraph) {
  1374         LEMON_ASSERT(false, "ReachedMap is not initialized");
  1375         return 0; // ignore warnings
  1376       }
  1377     };
  1378     /// \brief \ref named-templ-param "Named parameter" for setting
  1379     /// ReachedMap type.
  1380     ///
  1381     /// \ref named-templ-param "Named parameter" for setting ReachedMap type.
  1382     template <class T>
  1383     struct SetReachedMap : public BfsVisit< Digraph, Visitor,
  1384                                             SetReachedMapTraits<T> > {
  1385       typedef BfsVisit< Digraph, Visitor, SetReachedMapTraits<T> > Create;
  1386     };
  1387     ///@}
  1388 
  1389   public:
  1390 
  1391     /// \brief Constructor.
  1392     ///
  1393     /// Constructor.
  1394     ///
  1395     /// \param digraph The digraph the algorithm runs on.
  1396     /// \param visitor The visitor object of the algorithm.
  1397     BfsVisit(const Digraph& digraph, Visitor& visitor)
  1398       : _digraph(&digraph), _visitor(&visitor),
  1399         _reached(0), local_reached(false) {}
  1400 
  1401     /// \brief Destructor.
  1402     ~BfsVisit() {
  1403       if(local_reached) delete _reached;
  1404     }
  1405 
  1406     /// \brief Sets the map that indicates which nodes are reached.
  1407     ///
  1408     /// Sets the map that indicates which nodes are reached.
  1409     /// If you don't use this function before calling \ref run(Node) "run()"
  1410     /// or \ref init(), an instance will be allocated automatically.
  1411     /// The destructor deallocates this automatically allocated map,
  1412     /// of course.
  1413     /// \return <tt> (*this) </tt>
  1414     BfsVisit &reachedMap(ReachedMap &m) {
  1415       if(local_reached) {
  1416         delete _reached;
  1417         local_reached = false;
  1418       }
  1419       _reached = &m;
  1420       return *this;
  1421     }
  1422 
  1423   public:
  1424 
  1425     /// \name Execution Control
  1426     /// The simplest way to execute the BFS algorithm is to use one of the
  1427     /// member functions called \ref run(Node) "run()".\n
  1428     /// If you need more control on the execution, first you have to call
  1429     /// \ref init(), then you can add several source nodes with
  1430     /// \ref addSource(). Finally the actual path computation can be
  1431     /// performed with one of the \ref start() functions.
  1432 
  1433     /// @{
  1434 
  1435     /// \brief Initializes the internal data structures.
  1436     ///
  1437     /// Initializes the internal data structures.
  1438     void init() {
  1439       create_maps();
  1440       _list.resize(countNodes(*_digraph));
  1441       _list_front = _list_back = -1;
  1442       for (NodeIt u(*_digraph) ; u != INVALID ; ++u) {
  1443         _reached->set(u, false);
  1444       }
  1445     }
  1446 
  1447     /// \brief Adds a new source node.
  1448     ///
  1449     /// Adds a new source node to the set of nodes to be processed.
  1450     void addSource(Node s) {
  1451       if(!(*_reached)[s]) {
  1452           _reached->set(s,true);
  1453           _visitor->start(s);
  1454           _visitor->reach(s);
  1455           _list[++_list_back] = s;
  1456         }
  1457     }
  1458 
  1459     /// \brief Processes the next node.
  1460     ///
  1461     /// Processes the next node.
  1462     ///
  1463     /// \return The processed node.
  1464     ///
  1465     /// \pre The queue must not be empty.
  1466     Node processNextNode() {
  1467       Node n = _list[++_list_front];
  1468       _visitor->process(n);
  1469       Arc e;
  1470       for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
  1471         Node m = _digraph->target(e);
  1472         if (!(*_reached)[m]) {
  1473           _visitor->discover(e);
  1474           _visitor->reach(m);
  1475           _reached->set(m, true);
  1476           _list[++_list_back] = m;
  1477         } else {
  1478           _visitor->examine(e);
  1479         }
  1480       }
  1481       return n;
  1482     }
  1483 
  1484     /// \brief Processes the next node.
  1485     ///
  1486     /// Processes the next node and checks if the given target node
  1487     /// is reached. If the target node is reachable from the processed
  1488     /// node, then the \c reach parameter will be set to \c true.
  1489     ///
  1490     /// \param target The target node.
  1491     /// \retval reach Indicates if the target node is reached.
  1492     /// It should be initially \c false.
  1493     ///
  1494     /// \return The processed node.
  1495     ///
  1496     /// \pre The queue must not be empty.
  1497     Node processNextNode(Node target, bool& reach) {
  1498       Node n = _list[++_list_front];
  1499       _visitor->process(n);
  1500       Arc e;
  1501       for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
  1502         Node m = _digraph->target(e);
  1503         if (!(*_reached)[m]) {
  1504           _visitor->discover(e);
  1505           _visitor->reach(m);
  1506           _reached->set(m, true);
  1507           _list[++_list_back] = m;
  1508           reach = reach || (target == m);
  1509         } else {
  1510           _visitor->examine(e);
  1511         }
  1512       }
  1513       return n;
  1514     }
  1515 
  1516     /// \brief Processes the next node.
  1517     ///
  1518     /// Processes the next node and checks if at least one of reached
  1519     /// nodes has \c true value in the \c nm node map. If one node
  1520     /// with \c true value is reachable from the processed node, then the
  1521     /// \c rnode parameter will be set to the first of such nodes.
  1522     ///
  1523     /// \param nm A \c bool (or convertible) node map that indicates the
  1524     /// possible targets.
  1525     /// \retval rnode The reached target node.
  1526     /// It should be initially \c INVALID.
  1527     ///
  1528     /// \return The processed node.
  1529     ///
  1530     /// \pre The queue must not be empty.
  1531     template <typename NM>
  1532     Node processNextNode(const NM& nm, Node& rnode) {
  1533       Node n = _list[++_list_front];
  1534       _visitor->process(n);
  1535       Arc e;
  1536       for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
  1537         Node m = _digraph->target(e);
  1538         if (!(*_reached)[m]) {
  1539           _visitor->discover(e);
  1540           _visitor->reach(m);
  1541           _reached->set(m, true);
  1542           _list[++_list_back] = m;
  1543           if (nm[m] && rnode == INVALID) rnode = m;
  1544         } else {
  1545           _visitor->examine(e);
  1546         }
  1547       }
  1548       return n;
  1549     }
  1550 
  1551     /// \brief The next node to be processed.
  1552     ///
  1553     /// Returns the next node to be processed or \c INVALID if the queue
  1554     /// is empty.
  1555     Node nextNode() const {
  1556       return _list_front != _list_back ? _list[_list_front + 1] : INVALID;
  1557     }
  1558 
  1559     /// \brief Returns \c false if there are nodes
  1560     /// to be processed.
  1561     ///
  1562     /// Returns \c false if there are nodes
  1563     /// to be processed in the queue.
  1564     bool emptyQueue() const { return _list_front == _list_back; }
  1565 
  1566     /// \brief Returns the number of the nodes to be processed.
  1567     ///
  1568     /// Returns the number of the nodes to be processed in the queue.
  1569     int queueSize() const { return _list_back - _list_front; }
  1570 
  1571     /// \brief Executes the algorithm.
  1572     ///
  1573     /// Executes the algorithm.
  1574     ///
  1575     /// This method runs the %BFS algorithm from the root node(s)
  1576     /// in order to compute the shortest path to each node.
  1577     ///
  1578     /// The algorithm computes
  1579     /// - the shortest path tree (forest),
  1580     /// - the distance of each node from the root(s).
  1581     ///
  1582     /// \pre init() must be called and at least one root node should be added
  1583     /// with addSource() before using this function.
  1584     ///
  1585     /// \note <tt>b.start()</tt> is just a shortcut of the following code.
  1586     /// \code
  1587     ///   while ( !b.emptyQueue() ) {
  1588     ///     b.processNextNode();
  1589     ///   }
  1590     /// \endcode
  1591     void start() {
  1592       while ( !emptyQueue() ) processNextNode();
  1593     }
  1594 
  1595     /// \brief Executes the algorithm until the given target node is reached.
  1596     ///
  1597     /// Executes the algorithm until the given target node is reached.
  1598     ///
  1599     /// This method runs the %BFS algorithm from the root node(s)
  1600     /// in order to compute the shortest path to \c t.
  1601     ///
  1602     /// The algorithm computes
  1603     /// - the shortest path to \c t,
  1604     /// - the distance of \c t from the root(s).
  1605     ///
  1606     /// \pre init() must be called and at least one root node should be
  1607     /// added with addSource() before using this function.
  1608     ///
  1609     /// \note <tt>b.start(t)</tt> is just a shortcut of the following code.
  1610     /// \code
  1611     ///   bool reach = false;
  1612     ///   while ( !b.emptyQueue() && !reach ) {
  1613     ///     b.processNextNode(t, reach);
  1614     ///   }
  1615     /// \endcode
  1616     void start(Node t) {
  1617       bool reach = false;
  1618       while ( !emptyQueue() && !reach ) processNextNode(t, reach);
  1619     }
  1620 
  1621     /// \brief Executes the algorithm until a condition is met.
  1622     ///
  1623     /// Executes the algorithm until a condition is met.
  1624     ///
  1625     /// This method runs the %BFS algorithm from the root node(s) in
  1626     /// order to compute the shortest path to a node \c v with
  1627     /// <tt>nm[v]</tt> true, if such a node can be found.
  1628     ///
  1629     /// \param nm must be a bool (or convertible) node map. The
  1630     /// algorithm will stop when it reaches a node \c v with
  1631     /// <tt>nm[v]</tt> true.
  1632     ///
  1633     /// \return The reached node \c v with <tt>nm[v]</tt> true or
  1634     /// \c INVALID if no such node was found.
  1635     ///
  1636     /// \pre init() must be called and at least one root node should be
  1637     /// added with addSource() before using this function.
  1638     ///
  1639     /// \note <tt>b.start(nm)</tt> is just a shortcut of the following code.
  1640     /// \code
  1641     ///   Node rnode = INVALID;
  1642     ///   while ( !b.emptyQueue() && rnode == INVALID ) {
  1643     ///     b.processNextNode(nm, rnode);
  1644     ///   }
  1645     ///   return rnode;
  1646     /// \endcode
  1647     template <typename NM>
  1648     Node start(const NM &nm) {
  1649       Node rnode = INVALID;
  1650       while ( !emptyQueue() && rnode == INVALID ) {
  1651         processNextNode(nm, rnode);
  1652       }
  1653       return rnode;
  1654     }
  1655 
  1656     /// \brief Runs the algorithm from the given source node.
  1657     ///
  1658     /// This method runs the %BFS algorithm from node \c s
  1659     /// in order to compute the shortest path to each node.
  1660     ///
  1661     /// The algorithm computes
  1662     /// - the shortest path tree,
  1663     /// - the distance of each node from the root.
  1664     ///
  1665     /// \note <tt>b.run(s)</tt> is just a shortcut of the following code.
  1666     ///\code
  1667     ///   b.init();
  1668     ///   b.addSource(s);
  1669     ///   b.start();
  1670     ///\endcode
  1671     void run(Node s) {
  1672       init();
  1673       addSource(s);
  1674       start();
  1675     }
  1676 
  1677     /// \brief Finds the shortest path between \c s and \c t.
  1678     ///
  1679     /// This method runs the %BFS algorithm from node \c s
  1680     /// in order to compute the shortest path to node \c t
  1681     /// (it stops searching when \c t is processed).
  1682     ///
  1683     /// \return \c true if \c t is reachable form \c s.
  1684     ///
  1685     /// \note Apart from the return value, <tt>b.run(s,t)</tt> is just a
  1686     /// shortcut of the following code.
  1687     ///\code
  1688     ///   b.init();
  1689     ///   b.addSource(s);
  1690     ///   b.start(t);
  1691     ///\endcode
  1692     bool run(Node s,Node t) {
  1693       init();
  1694       addSource(s);
  1695       start(t);
  1696       return reached(t);
  1697     }
  1698 
  1699     /// \brief Runs the algorithm to visit all nodes in the digraph.
  1700     ///
  1701     /// This method runs the %BFS algorithm in order to
  1702     /// compute the shortest path to each node.
  1703     ///
  1704     /// The algorithm computes
  1705     /// - the shortest path tree (forest),
  1706     /// - the distance of each node from the root(s).
  1707     ///
  1708     /// \note <tt>b.run(s)</tt> is just a shortcut of the following code.
  1709     ///\code
  1710     ///  b.init();
  1711     ///  for (NodeIt n(gr); n != INVALID; ++n) {
  1712     ///    if (!b.reached(n)) {
  1713     ///      b.addSource(n);
  1714     ///      b.start();
  1715     ///    }
  1716     ///  }
  1717     ///\endcode
  1718     void run() {
  1719       init();
  1720       for (NodeIt it(*_digraph); it != INVALID; ++it) {
  1721         if (!reached(it)) {
  1722           addSource(it);
  1723           start();
  1724         }
  1725       }
  1726     }
  1727 
  1728     ///@}
  1729 
  1730     /// \name Query Functions
  1731     /// The results of the BFS algorithm can be obtained using these
  1732     /// functions.\n
  1733     /// Either \ref run(Node) "run()" or \ref start() should be called
  1734     /// before using them.
  1735 
  1736     ///@{
  1737 
  1738     /// \brief Checks if a node is reached from the root(s).
  1739     ///
  1740     /// Returns \c true if \c v is reached from the root(s).
  1741     ///
  1742     /// \pre Either \ref run(Node) "run()" or \ref init()
  1743     /// must be called before using this function.
  1744     bool reached(Node v) const { return (*_reached)[v]; }
  1745 
  1746     ///@}
  1747 
  1748   };
  1749 
  1750 } //END OF NAMESPACE LEMON
  1751 
  1752 #endif