lemon/bfs.h
author Balazs Dezso <deba@inf.elte.hu>
Sun, 30 Nov 2008 19:18:32 +0100
changeset 416 76287c8caa26
parent 301 9db8964f0cf6
child 405 6b9057cdcd8b
permissions -rw-r--r--
Reorganication of graph adaptors and doc improvements (#67)

- Moving to one file, lemon/adaptors.h
- Renamings
- Doc cleanings
     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) 2003-2008
     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.///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
    84     typedef typename Digraph::template NodeMap<bool> ReachedMap;
    85     ///Instantiates a ReachedMap.
    86 
    87     ///This function instantiates a ReachedMap.
    88     ///\param g is the digraph, to which
    89     ///we would like to define the ReachedMap.
    90     static ReachedMap *createReachedMap(const Digraph &g)
    91     {
    92       return new ReachedMap(g);
    93     }
    94 
    95     ///The type of the map that stores the distances of the nodes.
    96 
    97     ///The type of the map that stores the distances of the nodes.
    98     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
    99     typedef typename Digraph::template NodeMap<int> DistMap;
   100     ///Instantiates a DistMap.
   101 
   102     ///This function instantiates a DistMap.
   103     ///\param g is the digraph, to which we would like to define the
   104     ///DistMap.
   105     static DistMap *createDistMap(const Digraph &g)
   106     {
   107       return new DistMap(g);
   108     }
   109   };
   110 
   111   ///%BFS algorithm class.
   112 
   113   ///\ingroup search
   114   ///This class provides an efficient implementation of the %BFS algorithm.
   115   ///
   116   ///There is also a \ref bfs() "function-type interface" for the BFS
   117   ///algorithm, which is convenient in the simplier cases and it can be
   118   ///used easier.
   119   ///
   120   ///\tparam GR The type of the digraph the algorithm runs on.
   121   ///The default value is \ref ListDigraph. The value of GR is not used
   122   ///directly by \ref Bfs, it is only passed to \ref BfsDefaultTraits.
   123   ///\tparam TR Traits class to set various data types used by the algorithm.
   124   ///The default traits class is
   125   ///\ref BfsDefaultTraits "BfsDefaultTraits<GR>".
   126   ///See \ref BfsDefaultTraits for the documentation of
   127   ///a Bfs traits class.
   128 #ifdef DOXYGEN
   129   template <typename GR,
   130             typename TR>
   131 #else
   132   template <typename GR=ListDigraph,
   133             typename TR=BfsDefaultTraits<GR> >
   134 #endif
   135   class Bfs {
   136   public:
   137 
   138     ///The type of the digraph the algorithm runs on.
   139     typedef typename TR::Digraph Digraph;
   140 
   141     ///\brief The type of the map that stores the predecessor arcs of the
   142     ///shortest paths.
   143     typedef typename TR::PredMap PredMap;
   144     ///The type of the map that stores the distances of the nodes.
   145     typedef typename TR::DistMap DistMap;
   146     ///The type of the map that indicates which nodes are reached.
   147     typedef typename TR::ReachedMap ReachedMap;
   148     ///The type of the map that indicates which nodes are processed.
   149     typedef typename TR::ProcessedMap ProcessedMap;
   150     ///The type of the paths.
   151     typedef PredMapPath<Digraph, PredMap> Path;
   152 
   153     ///The traits class.
   154     typedef TR Traits;
   155 
   156   private:
   157 
   158     typedef typename Digraph::Node Node;
   159     typedef typename Digraph::NodeIt NodeIt;
   160     typedef typename Digraph::Arc Arc;
   161     typedef typename Digraph::OutArcIt OutArcIt;
   162 
   163     //Pointer to the underlying digraph.
   164     const Digraph *G;
   165     //Pointer to the map of predecessor arcs.
   166     PredMap *_pred;
   167     //Indicates if _pred is locally allocated (true) or not.
   168     bool local_pred;
   169     //Pointer to the map of distances.
   170     DistMap *_dist;
   171     //Indicates if _dist is locally allocated (true) or not.
   172     bool local_dist;
   173     //Pointer to the map of reached status of the nodes.
   174     ReachedMap *_reached;
   175     //Indicates if _reached is locally allocated (true) or not.
   176     bool local_reached;
   177     //Pointer to the map of processed status of the nodes.
   178     ProcessedMap *_processed;
   179     //Indicates if _processed is locally allocated (true) or not.
   180     bool local_processed;
   181 
   182     std::vector<typename Digraph::Node> _queue;
   183     int _queue_head,_queue_tail,_queue_next_dist;
   184     int _curr_dist;
   185 
   186     //Creates the maps if necessary.
   187     void create_maps()
   188     {
   189       if(!_pred) {
   190         local_pred = true;
   191         _pred = Traits::createPredMap(*G);
   192       }
   193       if(!_dist) {
   194         local_dist = true;
   195         _dist = Traits::createDistMap(*G);
   196       }
   197       if(!_reached) {
   198         local_reached = true;
   199         _reached = Traits::createReachedMap(*G);
   200       }
   201       if(!_processed) {
   202         local_processed = true;
   203         _processed = Traits::createProcessedMap(*G);
   204       }
   205     }
   206 
   207   protected:
   208 
   209     Bfs() {}
   210 
   211   public:
   212 
   213     typedef Bfs Create;
   214 
   215     ///\name Named template parameters
   216 
   217     ///@{
   218 
   219     template <class T>
   220     struct SetPredMapTraits : public Traits {
   221       typedef T PredMap;
   222       static PredMap *createPredMap(const Digraph &)
   223       {
   224         LEMON_ASSERT(false, "PredMap is not initialized");
   225         return 0; // ignore warnings
   226       }
   227     };
   228     ///\brief \ref named-templ-param "Named parameter" for setting
   229     ///PredMap type.
   230     ///
   231     ///\ref named-templ-param "Named parameter" for setting
   232     ///PredMap type.
   233     template <class T>
   234     struct SetPredMap : public Bfs< Digraph, SetPredMapTraits<T> > {
   235       typedef Bfs< Digraph, SetPredMapTraits<T> > Create;
   236     };
   237 
   238     template <class T>
   239     struct SetDistMapTraits : public Traits {
   240       typedef T DistMap;
   241       static DistMap *createDistMap(const Digraph &)
   242       {
   243         LEMON_ASSERT(false, "DistMap is not initialized");
   244         return 0; // ignore warnings
   245       }
   246     };
   247     ///\brief \ref named-templ-param "Named parameter" for setting
   248     ///DistMap type.
   249     ///
   250     ///\ref named-templ-param "Named parameter" for setting
   251     ///DistMap type.
   252     template <class T>
   253     struct SetDistMap : public Bfs< Digraph, SetDistMapTraits<T> > {
   254       typedef Bfs< Digraph, SetDistMapTraits<T> > Create;
   255     };
   256 
   257     template <class T>
   258     struct SetReachedMapTraits : public Traits {
   259       typedef T ReachedMap;
   260       static ReachedMap *createReachedMap(const Digraph &)
   261       {
   262         LEMON_ASSERT(false, "ReachedMap is not initialized");
   263         return 0; // ignore warnings
   264       }
   265     };
   266     ///\brief \ref named-templ-param "Named parameter" for setting
   267     ///ReachedMap type.
   268     ///
   269     ///\ref named-templ-param "Named parameter" for setting
   270     ///ReachedMap type.
   271     template <class T>
   272     struct SetReachedMap : public Bfs< Digraph, SetReachedMapTraits<T> > {
   273       typedef Bfs< Digraph, SetReachedMapTraits<T> > Create;
   274     };
   275 
   276     template <class T>
   277     struct SetProcessedMapTraits : public Traits {
   278       typedef T ProcessedMap;
   279       static ProcessedMap *createProcessedMap(const Digraph &)
   280       {
   281         LEMON_ASSERT(false, "ProcessedMap is not initialized");
   282         return 0; // ignore warnings
   283       }
   284     };
   285     ///\brief \ref named-templ-param "Named parameter" for setting
   286     ///ProcessedMap type.
   287     ///
   288     ///\ref named-templ-param "Named parameter" for setting
   289     ///ProcessedMap type.
   290     template <class T>
   291     struct SetProcessedMap : public Bfs< Digraph, SetProcessedMapTraits<T> > {
   292       typedef Bfs< Digraph, SetProcessedMapTraits<T> > Create;
   293     };
   294 
   295     struct SetStandardProcessedMapTraits : public Traits {
   296       typedef typename Digraph::template NodeMap<bool> ProcessedMap;
   297       static ProcessedMap *createProcessedMap(const Digraph &g)
   298       {
   299         return new ProcessedMap(g);
   300         return 0; // ignore warnings
   301       }
   302     };
   303     ///\brief \ref named-templ-param "Named parameter" for setting
   304     ///ProcessedMap type to be <tt>Digraph::NodeMap<bool></tt>.
   305     ///
   306     ///\ref named-templ-param "Named parameter" for setting
   307     ///ProcessedMap type to be <tt>Digraph::NodeMap<bool></tt>.
   308     ///If you don't set it explicitly, it will be automatically allocated.
   309     struct SetStandardProcessedMap :
   310       public Bfs< Digraph, SetStandardProcessedMapTraits > {
   311       typedef Bfs< Digraph, SetStandardProcessedMapTraits > Create;
   312     };
   313 
   314     ///@}
   315 
   316   public:
   317 
   318     ///Constructor.
   319 
   320     ///Constructor.
   321     ///\param g The digraph the algorithm runs on.
   322     Bfs(const Digraph &g) :
   323       G(&g),
   324       _pred(NULL), local_pred(false),
   325       _dist(NULL), local_dist(false),
   326       _reached(NULL), local_reached(false),
   327       _processed(NULL), local_processed(false)
   328     { }
   329 
   330     ///Destructor.
   331     ~Bfs()
   332     {
   333       if(local_pred) delete _pred;
   334       if(local_dist) delete _dist;
   335       if(local_reached) delete _reached;
   336       if(local_processed) delete _processed;
   337     }
   338 
   339     ///Sets the map that stores the predecessor arcs.
   340 
   341     ///Sets the map that stores the predecessor arcs.
   342     ///If you don't use this function before calling \ref run(),
   343     ///it will allocate one. The destructor deallocates this
   344     ///automatically allocated map, 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(),
   360     ///it will allocate one. The destructor deallocates this
   361     ///automatically allocated map, of course.
   362     ///\return <tt> (*this) </tt>
   363     Bfs &reachedMap(ReachedMap &m)
   364     {
   365       if(local_reached) {
   366         delete _reached;
   367         local_reached=false;
   368       }
   369       _reached = &m;
   370       return *this;
   371     }
   372 
   373     ///Sets the map that indicates which nodes are processed.
   374 
   375     ///Sets the map that indicates which nodes are processed.
   376     ///If you don't use this function before calling \ref run(),
   377     ///it will allocate one. The destructor deallocates this
   378     ///automatically allocated map, of course.
   379     ///\return <tt> (*this) </tt>
   380     Bfs &processedMap(ProcessedMap &m)
   381     {
   382       if(local_processed) {
   383         delete _processed;
   384         local_processed=false;
   385       }
   386       _processed = &m;
   387       return *this;
   388     }
   389 
   390     ///Sets the map that stores the distances of the nodes.
   391 
   392     ///Sets the map that stores the distances of the nodes calculated by
   393     ///the algorithm.
   394     ///If you don't use this function before calling \ref run(),
   395     ///it will allocate one. The destructor deallocates this
   396     ///automatically allocated map, of course.
   397     ///\return <tt> (*this) </tt>
   398     Bfs &distMap(DistMap &m)
   399     {
   400       if(local_dist) {
   401         delete _dist;
   402         local_dist=false;
   403       }
   404       _dist = &m;
   405       return *this;
   406     }
   407 
   408   public:
   409 
   410     ///\name Execution control
   411     ///The simplest way to execute the algorithm is to use
   412     ///one of the member functions called \ref lemon::Bfs::run() "run()".
   413     ///\n
   414     ///If you need more control on the execution, first you must call
   415     ///\ref lemon::Bfs::init() "init()", then you can add several source
   416     ///nodes with \ref lemon::Bfs::addSource() "addSource()".
   417     ///Finally \ref lemon::Bfs::start() "start()" will perform the
   418     ///actual path computation.
   419 
   420     ///@{
   421 
   422     ///Initializes the internal data structures.
   423 
   424     ///Initializes the internal data structures.
   425     ///
   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     ///\brief Returns \c false if there are nodes
   560     ///to be processed.
   561     ///
   562     ///Returns \c false if there are nodes
   563     ///to be processed in the queue.
   564     bool emptyQueue() const { return _queue_tail==_queue_head; }
   565 
   566     ///Returns the number of the nodes to be processed.
   567 
   568     ///Returns the number of the nodes to be processed 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 result of the %BFS algorithm can be obtained using these
   734     ///functions.\n
   735     ///Either \ref lemon::Bfs::run() "run()" or \ref lemon::Bfs::start()
   736     ///"start()" must be called 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 reachable from the root(s).
   745     ///
   746     ///\pre Either \ref run() or \ref start() must be called before
   747     ///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 reachable from the root(s), then
   755     ///the return value of this function is undefined.
   756     ///
   757     ///\pre Either \ref run() or \ref start() must be called before
   758     ///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 the root(s) to \c v. It is \c INVALID if \c v
   766     ///is not reachable 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() or \ref start() must be called before
   772     ///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 the root(s) to \c v. It is \c INVALID
   780     ///if \c v is not reachable 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() or \ref start() must be called before
   786     ///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() 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() 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 reachable from the root(s).
   811 
   812     ///Returns \c true if \c v is reachable from the root(s).
   813     ///\pre Either \ref run() or \ref start()
   814     ///must be called before using this function.
   815     bool reached(Node v) const { return (*_reached)[v]; }
   816 
   817     ///@}
   818   };
   819 
   820   ///Default traits class of bfs() function.
   821 
   822   ///Default traits class of bfs() function.
   823   ///\tparam GR Digraph type.
   824   template<class GR>
   825   struct BfsWizardDefaultTraits
   826   {
   827     ///The type of the digraph the algorithm runs on.
   828     typedef GR Digraph;
   829 
   830     ///\brief The type of the map that stores the predecessor
   831     ///arcs of the shortest paths.
   832     ///
   833     ///The type of the map that stores the predecessor
   834     ///arcs of the shortest paths.
   835     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   836     typedef typename Digraph::template NodeMap<typename Digraph::Arc> PredMap;
   837     ///Instantiates a PredMap.
   838 
   839     ///This function instantiates a PredMap.
   840     ///\param g is the digraph, to which we would like to define the
   841     ///PredMap.
   842     static PredMap *createPredMap(const Digraph &g)
   843     {
   844       return new PredMap(g);
   845     }
   846 
   847     ///The type of the map that indicates which nodes are processed.
   848 
   849     ///The type of the map that indicates which nodes are processed.
   850     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   851     ///By default it is a NullMap.
   852     typedef NullMap<typename Digraph::Node,bool> ProcessedMap;
   853     ///Instantiates a ProcessedMap.
   854 
   855     ///This function instantiates a ProcessedMap.
   856     ///\param g is the digraph, to which
   857     ///we would like to define the ProcessedMap.
   858 #ifdef DOXYGEN
   859     static ProcessedMap *createProcessedMap(const Digraph &g)
   860 #else
   861     static ProcessedMap *createProcessedMap(const Digraph &)
   862 #endif
   863     {
   864       return new ProcessedMap();
   865     }
   866 
   867     ///The type of the map that indicates which nodes are reached.
   868 
   869     ///The type of the map that indicates which nodes are reached.
   870     ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
   871     typedef typename Digraph::template NodeMap<bool> ReachedMap;
   872     ///Instantiates a ReachedMap.
   873 
   874     ///This function instantiates a ReachedMap.
   875     ///\param g is the digraph, to which
   876     ///we would like to define the ReachedMap.
   877     static ReachedMap *createReachedMap(const Digraph &g)
   878     {
   879       return new ReachedMap(g);
   880     }
   881 
   882     ///The type of the map that stores the distances of the nodes.
   883 
   884     ///The type of the map that stores the distances of the nodes.
   885     ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
   886     typedef typename Digraph::template NodeMap<int> DistMap;
   887     ///Instantiates a DistMap.
   888 
   889     ///This function instantiates a DistMap.
   890     ///\param g is the digraph, to which we would like to define
   891     ///the DistMap
   892     static DistMap *createDistMap(const Digraph &g)
   893     {
   894       return new DistMap(g);
   895     }
   896 
   897     ///The type of the shortest paths.
   898 
   899     ///The type of the shortest paths.
   900     ///It must meet the \ref concepts::Path "Path" concept.
   901     typedef lemon::Path<Digraph> Path;
   902   };
   903 
   904   /// Default traits class used by BfsWizard
   905 
   906   /// To make it easier to use Bfs algorithm
   907   /// we have created a wizard class.
   908   /// This \ref BfsWizard class needs default traits,
   909   /// as well as the \ref Bfs class.
   910   /// The \ref BfsWizardBase is a class to be the default traits of the
   911   /// \ref BfsWizard class.
   912   template<class GR>
   913   class BfsWizardBase : public BfsWizardDefaultTraits<GR>
   914   {
   915 
   916     typedef BfsWizardDefaultTraits<GR> Base;
   917   protected:
   918     //The type of the nodes in the digraph.
   919     typedef typename Base::Digraph::Node Node;
   920 
   921     //Pointer to the digraph the algorithm runs on.
   922     void *_g;
   923     //Pointer to the map of reached nodes.
   924     void *_reached;
   925     //Pointer to the map of processed nodes.
   926     void *_processed;
   927     //Pointer to the map of predecessors arcs.
   928     void *_pred;
   929     //Pointer to the map of distances.
   930     void *_dist;
   931     //Pointer to the shortest path to the target node.
   932     void *_path;
   933     //Pointer to the distance of the target node.
   934     int *_di;
   935 
   936     public:
   937     /// Constructor.
   938 
   939     /// This constructor does not require parameters, therefore it initiates
   940     /// all of the attributes to \c 0.
   941     BfsWizardBase() : _g(0), _reached(0), _processed(0), _pred(0),
   942                       _dist(0), _path(0), _di(0) {}
   943 
   944     /// Constructor.
   945 
   946     /// This constructor requires one parameter,
   947     /// others are initiated to \c 0.
   948     /// \param g The digraph the algorithm runs on.
   949     BfsWizardBase(const GR &g) :
   950       _g(reinterpret_cast<void*>(const_cast<GR*>(&g))),
   951       _reached(0), _processed(0), _pred(0), _dist(0),  _path(0), _di(0) {}
   952 
   953   };
   954 
   955   /// Auxiliary class for the function-type interface of BFS algorithm.
   956 
   957   /// This auxiliary class is created to implement the
   958   /// \ref bfs() "function-type interface" of \ref Bfs algorithm.
   959   /// It does not have own \ref run() method, it uses the functions
   960   /// and features of the plain \ref Bfs.
   961   ///
   962   /// This class should only be used through the \ref bfs() function,
   963   /// which makes it easier to use the algorithm.
   964   template<class TR>
   965   class BfsWizard : public TR
   966   {
   967     typedef TR Base;
   968 
   969     ///The type of the digraph the algorithm runs on.
   970     typedef typename TR::Digraph Digraph;
   971 
   972     typedef typename Digraph::Node Node;
   973     typedef typename Digraph::NodeIt NodeIt;
   974     typedef typename Digraph::Arc Arc;
   975     typedef typename Digraph::OutArcIt OutArcIt;
   976 
   977     ///\brief The type of the map that stores the predecessor
   978     ///arcs of the shortest paths.
   979     typedef typename TR::PredMap PredMap;
   980     ///\brief The type of the map that stores the distances of the nodes.
   981     typedef typename TR::DistMap DistMap;
   982     ///\brief The type of the map that indicates which nodes are reached.
   983     typedef typename TR::ReachedMap ReachedMap;
   984     ///\brief The type of the map that indicates which nodes are processed.
   985     typedef typename TR::ProcessedMap ProcessedMap;
   986     ///The type of the shortest paths
   987     typedef typename TR::Path Path;
   988 
   989   public:
   990 
   991     /// Constructor.
   992     BfsWizard() : TR() {}
   993 
   994     /// Constructor that requires parameters.
   995 
   996     /// Constructor that requires parameters.
   997     /// These parameters will be the default values for the traits class.
   998     /// \param g The digraph the algorithm runs on.
   999     BfsWizard(const Digraph &g) :
  1000       TR(g) {}
  1001 
  1002     ///Copy constructor
  1003     BfsWizard(const TR &b) : TR(b) {}
  1004 
  1005     ~BfsWizard() {}
  1006 
  1007     ///Runs BFS algorithm from the given source node.
  1008 
  1009     ///This method runs BFS algorithm from node \c s
  1010     ///in order to compute the shortest path to each node.
  1011     void run(Node s)
  1012     {
  1013       Bfs<Digraph,TR> alg(*reinterpret_cast<const Digraph*>(Base::_g));
  1014       if (Base::_pred)
  1015         alg.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
  1016       if (Base::_dist)
  1017         alg.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
  1018       if (Base::_reached)
  1019         alg.reachedMap(*reinterpret_cast<ReachedMap*>(Base::_reached));
  1020       if (Base::_processed)
  1021         alg.processedMap(*reinterpret_cast<ProcessedMap*>(Base::_processed));
  1022       if (s!=INVALID)
  1023         alg.run(s);
  1024       else
  1025         alg.run();
  1026     }
  1027 
  1028     ///Finds the shortest path between \c s and \c t.
  1029 
  1030     ///This method runs BFS algorithm from node \c s
  1031     ///in order to compute the shortest path to node \c t
  1032     ///(it stops searching when \c t is processed).
  1033     ///
  1034     ///\return \c true if \c t is reachable form \c s.
  1035     bool run(Node s, Node t)
  1036     {
  1037       Bfs<Digraph,TR> alg(*reinterpret_cast<const Digraph*>(Base::_g));
  1038       if (Base::_pred)
  1039         alg.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
  1040       if (Base::_dist)
  1041         alg.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
  1042       if (Base::_reached)
  1043         alg.reachedMap(*reinterpret_cast<ReachedMap*>(Base::_reached));
  1044       if (Base::_processed)
  1045         alg.processedMap(*reinterpret_cast<ProcessedMap*>(Base::_processed));
  1046       alg.run(s,t);
  1047       if (Base::_path)
  1048         *reinterpret_cast<Path*>(Base::_path) = alg.path(t);
  1049       if (Base::_di)
  1050         *Base::_di = alg.dist(t);
  1051       return alg.reached(t);
  1052     }
  1053 
  1054     ///Runs BFS algorithm to visit all nodes in the digraph.
  1055 
  1056     ///This method runs BFS algorithm in order to compute
  1057     ///the shortest path to each node.
  1058     void run()
  1059     {
  1060       run(INVALID);
  1061     }
  1062 
  1063     template<class T>
  1064     struct SetPredMapBase : public Base {
  1065       typedef T PredMap;
  1066       static PredMap *createPredMap(const Digraph &) { return 0; };
  1067       SetPredMapBase(const TR &b) : TR(b) {}
  1068     };
  1069     ///\brief \ref named-func-param "Named parameter"
  1070     ///for setting PredMap object.
  1071     ///
  1072     ///\ref named-func-param "Named parameter"
  1073     ///for setting PredMap object.
  1074     template<class T>
  1075     BfsWizard<SetPredMapBase<T> > predMap(const T &t)
  1076     {
  1077       Base::_pred=reinterpret_cast<void*>(const_cast<T*>(&t));
  1078       return BfsWizard<SetPredMapBase<T> >(*this);
  1079     }
  1080 
  1081     template<class T>
  1082     struct SetReachedMapBase : public Base {
  1083       typedef T ReachedMap;
  1084       static ReachedMap *createReachedMap(const Digraph &) { return 0; };
  1085       SetReachedMapBase(const TR &b) : TR(b) {}
  1086     };
  1087     ///\brief \ref named-func-param "Named parameter"
  1088     ///for setting ReachedMap object.
  1089     ///
  1090     /// \ref named-func-param "Named parameter"
  1091     ///for setting ReachedMap object.
  1092     template<class T>
  1093     BfsWizard<SetReachedMapBase<T> > reachedMap(const T &t)
  1094     {
  1095       Base::_reached=reinterpret_cast<void*>(const_cast<T*>(&t));
  1096       return BfsWizard<SetReachedMapBase<T> >(*this);
  1097     }
  1098 
  1099     template<class T>
  1100     struct SetDistMapBase : public Base {
  1101       typedef T DistMap;
  1102       static DistMap *createDistMap(const Digraph &) { return 0; };
  1103       SetDistMapBase(const TR &b) : TR(b) {}
  1104     };
  1105     ///\brief \ref named-func-param "Named parameter"
  1106     ///for setting DistMap object.
  1107     ///
  1108     /// \ref named-func-param "Named parameter"
  1109     ///for setting DistMap object.
  1110     template<class T>
  1111     BfsWizard<SetDistMapBase<T> > distMap(const T &t)
  1112     {
  1113       Base::_dist=reinterpret_cast<void*>(const_cast<T*>(&t));
  1114       return BfsWizard<SetDistMapBase<T> >(*this);
  1115     }
  1116 
  1117     template<class T>
  1118     struct SetProcessedMapBase : public Base {
  1119       typedef T ProcessedMap;
  1120       static ProcessedMap *createProcessedMap(const Digraph &) { return 0; };
  1121       SetProcessedMapBase(const TR &b) : TR(b) {}
  1122     };
  1123     ///\brief \ref named-func-param "Named parameter"
  1124     ///for setting ProcessedMap object.
  1125     ///
  1126     /// \ref named-func-param "Named parameter"
  1127     ///for setting ProcessedMap object.
  1128     template<class T>
  1129     BfsWizard<SetProcessedMapBase<T> > processedMap(const T &t)
  1130     {
  1131       Base::_processed=reinterpret_cast<void*>(const_cast<T*>(&t));
  1132       return BfsWizard<SetProcessedMapBase<T> >(*this);
  1133     }
  1134 
  1135     template<class T>
  1136     struct SetPathBase : public Base {
  1137       typedef T Path;
  1138       SetPathBase(const TR &b) : TR(b) {}
  1139     };
  1140     ///\brief \ref named-func-param "Named parameter"
  1141     ///for getting the shortest path to the target node.
  1142     ///
  1143     ///\ref named-func-param "Named parameter"
  1144     ///for getting the shortest path to the target node.
  1145     template<class T>
  1146     BfsWizard<SetPathBase<T> > path(const T &t)
  1147     {
  1148       Base::_path=reinterpret_cast<void*>(const_cast<T*>(&t));
  1149       return BfsWizard<SetPathBase<T> >(*this);
  1150     }
  1151 
  1152     ///\brief \ref named-func-param "Named parameter"
  1153     ///for getting the distance of the target node.
  1154     ///
  1155     ///\ref named-func-param "Named parameter"
  1156     ///for getting the distance of the target node.
  1157     BfsWizard dist(const int &d)
  1158     {
  1159       Base::_di=const_cast<int*>(&d);
  1160       return *this;
  1161     }
  1162 
  1163   };
  1164 
  1165   ///Function-type interface for BFS algorithm.
  1166 
  1167   /// \ingroup search
  1168   ///Function-type interface for BFS algorithm.
  1169   ///
  1170   ///This function also has several \ref named-func-param "named parameters",
  1171   ///they are declared as the members of class \ref BfsWizard.
  1172   ///The following examples show how to use these parameters.
  1173   ///\code
  1174   ///  // Compute shortest path from node s to each node
  1175   ///  bfs(g).predMap(preds).distMap(dists).run(s);
  1176   ///
  1177   ///  // Compute shortest path from s to t
  1178   ///  bool reached = bfs(g).path(p).dist(d).run(s,t);
  1179   ///\endcode
  1180   ///\warning Don't forget to put the \ref BfsWizard::run() "run()"
  1181   ///to the end of the parameter list.
  1182   ///\sa BfsWizard
  1183   ///\sa Bfs
  1184   template<class GR>
  1185   BfsWizard<BfsWizardBase<GR> >
  1186   bfs(const GR &digraph)
  1187   {
  1188     return BfsWizard<BfsWizardBase<GR> >(digraph);
  1189   }
  1190 
  1191 #ifdef DOXYGEN
  1192   /// \brief Visitor class for BFS.
  1193   ///
  1194   /// This class defines the interface of the BfsVisit events, and
  1195   /// it could be the base of a real visitor class.
  1196   template <typename _Digraph>
  1197   struct BfsVisitor {
  1198     typedef _Digraph Digraph;
  1199     typedef typename Digraph::Arc Arc;
  1200     typedef typename Digraph::Node Node;
  1201     /// \brief Called for the source node(s) of the BFS.
  1202     ///
  1203     /// This function is called for the source node(s) of the BFS.
  1204     void start(const Node& node) {}
  1205     /// \brief Called when a node is reached first time.
  1206     ///
  1207     /// This function is called when a node is reached first time.
  1208     void reach(const Node& node) {}
  1209     /// \brief Called when a node is processed.
  1210     ///
  1211     /// This function is called when a node is processed.
  1212     void process(const Node& node) {}
  1213     /// \brief Called when an arc reaches a new node.
  1214     ///
  1215     /// This function is called when the BFS finds an arc whose target node
  1216     /// is not reached yet.
  1217     void discover(const Arc& arc) {}
  1218     /// \brief Called when an arc is examined but its target node is
  1219     /// already discovered.
  1220     ///
  1221     /// This function is called when an arc is examined but its target node is
  1222     /// already discovered.
  1223     void examine(const Arc& arc) {}
  1224   };
  1225 #else
  1226   template <typename _Digraph>
  1227   struct BfsVisitor {
  1228     typedef _Digraph Digraph;
  1229     typedef typename Digraph::Arc Arc;
  1230     typedef typename Digraph::Node Node;
  1231     void start(const Node&) {}
  1232     void reach(const Node&) {}
  1233     void process(const Node&) {}
  1234     void discover(const Arc&) {}
  1235     void examine(const Arc&) {}
  1236 
  1237     template <typename _Visitor>
  1238     struct Constraints {
  1239       void constraints() {
  1240         Arc arc;
  1241         Node node;
  1242         visitor.start(node);
  1243         visitor.reach(node);
  1244         visitor.process(node);
  1245         visitor.discover(arc);
  1246         visitor.examine(arc);
  1247       }
  1248       _Visitor& visitor;
  1249     };
  1250   };
  1251 #endif
  1252 
  1253   /// \brief Default traits class of BfsVisit class.
  1254   ///
  1255   /// Default traits class of BfsVisit class.
  1256   /// \tparam _Digraph The type of the digraph the algorithm runs on.
  1257   template<class _Digraph>
  1258   struct BfsVisitDefaultTraits {
  1259 
  1260     /// \brief The type of the digraph the algorithm runs on.
  1261     typedef _Digraph Digraph;
  1262 
  1263     /// \brief The type of the map that indicates which nodes are reached.
  1264     ///
  1265     /// The type of the map that indicates which nodes are reached.
  1266     /// It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
  1267     typedef typename Digraph::template NodeMap<bool> ReachedMap;
  1268 
  1269     /// \brief Instantiates a ReachedMap.
  1270     ///
  1271     /// This function instantiates a ReachedMap.
  1272     /// \param digraph is the digraph, to which
  1273     /// we would like to define the ReachedMap.
  1274     static ReachedMap *createReachedMap(const Digraph &digraph) {
  1275       return new ReachedMap(digraph);
  1276     }
  1277 
  1278   };
  1279 
  1280   /// \ingroup search
  1281   ///
  1282   /// \brief %BFS algorithm class with visitor interface.
  1283   ///
  1284   /// This class provides an efficient implementation of the %BFS algorithm
  1285   /// with visitor interface.
  1286   ///
  1287   /// The %BfsVisit class provides an alternative interface to the Bfs
  1288   /// class. It works with callback mechanism, the BfsVisit object calls
  1289   /// the member functions of the \c Visitor class on every BFS event.
  1290   ///
  1291   /// This interface of the BFS algorithm should be used in special cases
  1292   /// when extra actions have to be performed in connection with certain
  1293   /// events of the BFS algorithm. Otherwise consider to use Bfs or bfs()
  1294   /// instead.
  1295   ///
  1296   /// \tparam _Digraph The type of the digraph the algorithm runs on.
  1297   /// The default value is
  1298   /// \ref ListDigraph. The value of _Digraph is not used directly by
  1299   /// \ref BfsVisit, it is only passed to \ref BfsVisitDefaultTraits.
  1300   /// \tparam _Visitor The Visitor type that is used by the algorithm.
  1301   /// \ref BfsVisitor "BfsVisitor<_Digraph>" is an empty visitor, which
  1302   /// does not observe the BFS events. If you want to observe the BFS
  1303   /// events, you should implement your own visitor class.
  1304   /// \tparam _Traits Traits class to set various data types used by the
  1305   /// algorithm. The default traits class is
  1306   /// \ref BfsVisitDefaultTraits "BfsVisitDefaultTraits<_Digraph>".
  1307   /// See \ref BfsVisitDefaultTraits for the documentation of
  1308   /// a BFS visit traits class.
  1309 #ifdef DOXYGEN
  1310   template <typename _Digraph, typename _Visitor, typename _Traits>
  1311 #else
  1312   template <typename _Digraph = ListDigraph,
  1313             typename _Visitor = BfsVisitor<_Digraph>,
  1314             typename _Traits = BfsVisitDefaultTraits<_Digraph> >
  1315 #endif
  1316   class BfsVisit {
  1317   public:
  1318 
  1319     ///The traits class.
  1320     typedef _Traits Traits;
  1321 
  1322     ///The type of the digraph the algorithm runs on.
  1323     typedef typename Traits::Digraph Digraph;
  1324 
  1325     ///The visitor type used by the algorithm.
  1326     typedef _Visitor Visitor;
  1327 
  1328     ///The type of the map that indicates which nodes are reached.
  1329     typedef typename Traits::ReachedMap ReachedMap;
  1330 
  1331   private:
  1332 
  1333     typedef typename Digraph::Node Node;
  1334     typedef typename Digraph::NodeIt NodeIt;
  1335     typedef typename Digraph::Arc Arc;
  1336     typedef typename Digraph::OutArcIt OutArcIt;
  1337 
  1338     //Pointer to the underlying digraph.
  1339     const Digraph *_digraph;
  1340     //Pointer to the visitor object.
  1341     Visitor *_visitor;
  1342     //Pointer to the map of reached status of the nodes.
  1343     ReachedMap *_reached;
  1344     //Indicates if _reached is locally allocated (true) or not.
  1345     bool local_reached;
  1346 
  1347     std::vector<typename Digraph::Node> _list;
  1348     int _list_front, _list_back;
  1349 
  1350     //Creates the maps if necessary.
  1351     void create_maps() {
  1352       if(!_reached) {
  1353         local_reached = true;
  1354         _reached = Traits::createReachedMap(*_digraph);
  1355       }
  1356     }
  1357 
  1358   protected:
  1359 
  1360     BfsVisit() {}
  1361 
  1362   public:
  1363 
  1364     typedef BfsVisit Create;
  1365 
  1366     /// \name Named template parameters
  1367 
  1368     ///@{
  1369     template <class T>
  1370     struct SetReachedMapTraits : public Traits {
  1371       typedef T ReachedMap;
  1372       static ReachedMap *createReachedMap(const Digraph &digraph) {
  1373         LEMON_ASSERT(false, "ReachedMap is not initialized");
  1374         return 0; // ignore warnings
  1375       }
  1376     };
  1377     /// \brief \ref named-templ-param "Named parameter" for setting
  1378     /// ReachedMap type.
  1379     ///
  1380     /// \ref named-templ-param "Named parameter" for setting ReachedMap type.
  1381     template <class T>
  1382     struct SetReachedMap : public BfsVisit< Digraph, Visitor,
  1383                                             SetReachedMapTraits<T> > {
  1384       typedef BfsVisit< Digraph, Visitor, SetReachedMapTraits<T> > Create;
  1385     };
  1386     ///@}
  1387 
  1388   public:
  1389 
  1390     /// \brief Constructor.
  1391     ///
  1392     /// Constructor.
  1393     ///
  1394     /// \param digraph The digraph the algorithm runs on.
  1395     /// \param visitor The visitor object of the algorithm.
  1396     BfsVisit(const Digraph& digraph, Visitor& visitor)
  1397       : _digraph(&digraph), _visitor(&visitor),
  1398         _reached(0), local_reached(false) {}
  1399 
  1400     /// \brief Destructor.
  1401     ~BfsVisit() {
  1402       if(local_reached) delete _reached;
  1403     }
  1404 
  1405     /// \brief Sets the map that indicates which nodes are reached.
  1406     ///
  1407     /// Sets the map that indicates which nodes are reached.
  1408     /// If you don't use this function before calling \ref run(),
  1409     /// it will allocate one. The destructor deallocates this
  1410     /// automatically allocated map, of course.
  1411     /// \return <tt> (*this) </tt>
  1412     BfsVisit &reachedMap(ReachedMap &m) {
  1413       if(local_reached) {
  1414         delete _reached;
  1415         local_reached = false;
  1416       }
  1417       _reached = &m;
  1418       return *this;
  1419     }
  1420 
  1421   public:
  1422 
  1423     /// \name Execution control
  1424     /// The simplest way to execute the algorithm is to use
  1425     /// one of the member functions called \ref lemon::BfsVisit::run()
  1426     /// "run()".
  1427     /// \n
  1428     /// If you need more control on the execution, first you must call
  1429     /// \ref lemon::BfsVisit::init() "init()", then you can add several
  1430     /// source nodes with \ref lemon::BfsVisit::addSource() "addSource()".
  1431     /// Finally \ref lemon::BfsVisit::start() "start()" will perform the
  1432     /// actual path computation.
  1433 
  1434     /// @{
  1435 
  1436     /// \brief Initializes the internal data structures.
  1437     ///
  1438     /// Initializes the internal data structures.
  1439     void init() {
  1440       create_maps();
  1441       _list.resize(countNodes(*_digraph));
  1442       _list_front = _list_back = -1;
  1443       for (NodeIt u(*_digraph) ; u != INVALID ; ++u) {
  1444         _reached->set(u, false);
  1445       }
  1446     }
  1447 
  1448     /// \brief Adds a new source node.
  1449     ///
  1450     /// Adds a new source node to the set of nodes to be processed.
  1451     void addSource(Node s) {
  1452       if(!(*_reached)[s]) {
  1453           _reached->set(s,true);
  1454           _visitor->start(s);
  1455           _visitor->reach(s);
  1456           _list[++_list_back] = s;
  1457         }
  1458     }
  1459 
  1460     /// \brief Processes the next node.
  1461     ///
  1462     /// Processes the next node.
  1463     ///
  1464     /// \return The processed node.
  1465     ///
  1466     /// \pre The queue must not be empty.
  1467     Node processNextNode() {
  1468       Node n = _list[++_list_front];
  1469       _visitor->process(n);
  1470       Arc e;
  1471       for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
  1472         Node m = _digraph->target(e);
  1473         if (!(*_reached)[m]) {
  1474           _visitor->discover(e);
  1475           _visitor->reach(m);
  1476           _reached->set(m, true);
  1477           _list[++_list_back] = m;
  1478         } else {
  1479           _visitor->examine(e);
  1480         }
  1481       }
  1482       return n;
  1483     }
  1484 
  1485     /// \brief Processes the next node.
  1486     ///
  1487     /// Processes the next node and checks if the given target node
  1488     /// is reached. If the target node is reachable from the processed
  1489     /// node, then the \c reach parameter will be set to \c true.
  1490     ///
  1491     /// \param target The target node.
  1492     /// \retval reach Indicates if the target node is reached.
  1493     /// It should be initially \c false.
  1494     ///
  1495     /// \return The processed node.
  1496     ///
  1497     /// \pre The queue must not be empty.
  1498     Node processNextNode(Node target, bool& reach) {
  1499       Node n = _list[++_list_front];
  1500       _visitor->process(n);
  1501       Arc e;
  1502       for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
  1503         Node m = _digraph->target(e);
  1504         if (!(*_reached)[m]) {
  1505           _visitor->discover(e);
  1506           _visitor->reach(m);
  1507           _reached->set(m, true);
  1508           _list[++_list_back] = m;
  1509           reach = reach || (target == m);
  1510         } else {
  1511           _visitor->examine(e);
  1512         }
  1513       }
  1514       return n;
  1515     }
  1516 
  1517     /// \brief Processes the next node.
  1518     ///
  1519     /// Processes the next node and checks if at least one of reached
  1520     /// nodes has \c true value in the \c nm node map. If one node
  1521     /// with \c true value is reachable from the processed node, then the
  1522     /// \c rnode parameter will be set to the first of such nodes.
  1523     ///
  1524     /// \param nm A \c bool (or convertible) node map that indicates the
  1525     /// possible targets.
  1526     /// \retval rnode The reached target node.
  1527     /// It should be initially \c INVALID.
  1528     ///
  1529     /// \return The processed node.
  1530     ///
  1531     /// \pre The queue must not be empty.
  1532     template <typename NM>
  1533     Node processNextNode(const NM& nm, Node& rnode) {
  1534       Node n = _list[++_list_front];
  1535       _visitor->process(n);
  1536       Arc e;
  1537       for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
  1538         Node m = _digraph->target(e);
  1539         if (!(*_reached)[m]) {
  1540           _visitor->discover(e);
  1541           _visitor->reach(m);
  1542           _reached->set(m, true);
  1543           _list[++_list_back] = m;
  1544           if (nm[m] && rnode == INVALID) rnode = m;
  1545         } else {
  1546           _visitor->examine(e);
  1547         }
  1548       }
  1549       return n;
  1550     }
  1551 
  1552     /// \brief The next node to be processed.
  1553     ///
  1554     /// Returns the next node to be processed or \c INVALID if the queue
  1555     /// is empty.
  1556     Node nextNode() const {
  1557       return _list_front != _list_back ? _list[_list_front + 1] : INVALID;
  1558     }
  1559 
  1560     /// \brief Returns \c false if there are nodes
  1561     /// to be processed.
  1562     ///
  1563     /// Returns \c false if there are nodes
  1564     /// to be processed in the queue.
  1565     bool emptyQueue() const { return _list_front == _list_back; }
  1566 
  1567     /// \brief Returns the number of the nodes to be processed.
  1568     ///
  1569     /// Returns the number of the nodes to be processed in the queue.
  1570     int queueSize() const { return _list_back - _list_front; }
  1571 
  1572     /// \brief Executes the algorithm.
  1573     ///
  1574     /// Executes the algorithm.
  1575     ///
  1576     /// This method runs the %BFS algorithm from the root node(s)
  1577     /// in order to compute the shortest path to each node.
  1578     ///
  1579     /// The algorithm computes
  1580     /// - the shortest path tree (forest),
  1581     /// - the distance of each node from the root(s).
  1582     ///
  1583     /// \pre init() must be called and at least one root node should be added
  1584     /// with addSource() before using this function.
  1585     ///
  1586     /// \note <tt>b.start()</tt> is just a shortcut of the following code.
  1587     /// \code
  1588     ///   while ( !b.emptyQueue() ) {
  1589     ///     b.processNextNode();
  1590     ///   }
  1591     /// \endcode
  1592     void start() {
  1593       while ( !emptyQueue() ) processNextNode();
  1594     }
  1595 
  1596     /// \brief Executes the algorithm until the given target node is reached.
  1597     ///
  1598     /// Executes the algorithm until the given target node is reached.
  1599     ///
  1600     /// This method runs the %BFS algorithm from the root node(s)
  1601     /// in order to compute the shortest path to \c t.
  1602     ///
  1603     /// The algorithm computes
  1604     /// - the shortest path to \c t,
  1605     /// - the distance of \c t from the root(s).
  1606     ///
  1607     /// \pre init() must be called and at least one root node should be
  1608     /// added with addSource() before using this function.
  1609     ///
  1610     /// \note <tt>b.start(t)</tt> is just a shortcut of the following code.
  1611     /// \code
  1612     ///   bool reach = false;
  1613     ///   while ( !b.emptyQueue() && !reach ) {
  1614     ///     b.processNextNode(t, reach);
  1615     ///   }
  1616     /// \endcode
  1617     void start(Node t) {
  1618       bool reach = false;
  1619       while ( !emptyQueue() && !reach ) processNextNode(t, reach);
  1620     }
  1621 
  1622     /// \brief Executes the algorithm until a condition is met.
  1623     ///
  1624     /// Executes the algorithm until a condition is met.
  1625     ///
  1626     /// This method runs the %BFS algorithm from the root node(s) in
  1627     /// order to compute the shortest path to a node \c v with
  1628     /// <tt>nm[v]</tt> true, if such a node can be found.
  1629     ///
  1630     /// \param nm must be a bool (or convertible) node map. The
  1631     /// algorithm will stop when it reaches a node \c v with
  1632     /// <tt>nm[v]</tt> true.
  1633     ///
  1634     /// \return The reached node \c v with <tt>nm[v]</tt> true or
  1635     /// \c INVALID if no such node was found.
  1636     ///
  1637     /// \pre init() must be called and at least one root node should be
  1638     /// added with addSource() before using this function.
  1639     ///
  1640     /// \note <tt>b.start(nm)</tt> is just a shortcut of the following code.
  1641     /// \code
  1642     ///   Node rnode = INVALID;
  1643     ///   while ( !b.emptyQueue() && rnode == INVALID ) {
  1644     ///     b.processNextNode(nm, rnode);
  1645     ///   }
  1646     ///   return rnode;
  1647     /// \endcode
  1648     template <typename NM>
  1649     Node start(const NM &nm) {
  1650       Node rnode = INVALID;
  1651       while ( !emptyQueue() && rnode == INVALID ) {
  1652         processNextNode(nm, rnode);
  1653       }
  1654       return rnode;
  1655     }
  1656 
  1657     /// \brief Runs the algorithm from the given source node.
  1658     ///
  1659     /// This method runs the %BFS algorithm from node \c s
  1660     /// in order to compute the shortest path to each node.
  1661     ///
  1662     /// The algorithm computes
  1663     /// - the shortest path tree,
  1664     /// - the distance of each node from the root.
  1665     ///
  1666     /// \note <tt>b.run(s)</tt> is just a shortcut of the following code.
  1667     ///\code
  1668     ///   b.init();
  1669     ///   b.addSource(s);
  1670     ///   b.start();
  1671     ///\endcode
  1672     void run(Node s) {
  1673       init();
  1674       addSource(s);
  1675       start();
  1676     }
  1677 
  1678     /// \brief Finds the shortest path between \c s and \c t.
  1679     ///
  1680     /// This method runs the %BFS algorithm from node \c s
  1681     /// in order to compute the shortest path to node \c t
  1682     /// (it stops searching when \c t is processed).
  1683     ///
  1684     /// \return \c true if \c t is reachable form \c s.
  1685     ///
  1686     /// \note Apart from the return value, <tt>b.run(s,t)</tt> is just a
  1687     /// shortcut of the following code.
  1688     ///\code
  1689     ///   b.init();
  1690     ///   b.addSource(s);
  1691     ///   b.start(t);
  1692     ///\endcode
  1693     bool run(Node s,Node t) {
  1694       init();
  1695       addSource(s);
  1696       start(t);
  1697       return reached(t);
  1698     }
  1699 
  1700     /// \brief Runs the algorithm to visit all nodes in the digraph.
  1701     ///
  1702     /// This method runs the %BFS algorithm in order to
  1703     /// compute the shortest path to each node.
  1704     ///
  1705     /// The algorithm computes
  1706     /// - the shortest path tree (forest),
  1707     /// - the distance of each node from the root(s).
  1708     ///
  1709     /// \note <tt>b.run(s)</tt> is just a shortcut of the following code.
  1710     ///\code
  1711     ///  b.init();
  1712     ///  for (NodeIt n(gr); n != INVALID; ++n) {
  1713     ///    if (!b.reached(n)) {
  1714     ///      b.addSource(n);
  1715     ///      b.start();
  1716     ///    }
  1717     ///  }
  1718     ///\endcode
  1719     void run() {
  1720       init();
  1721       for (NodeIt it(*_digraph); it != INVALID; ++it) {
  1722         if (!reached(it)) {
  1723           addSource(it);
  1724           start();
  1725         }
  1726       }
  1727     }
  1728 
  1729     ///@}
  1730 
  1731     /// \name Query Functions
  1732     /// The result of the %BFS algorithm can be obtained using these
  1733     /// functions.\n
  1734     /// Either \ref lemon::BfsVisit::run() "run()" or
  1735     /// \ref lemon::BfsVisit::start() "start()" must be called before
  1736     /// using them.
  1737     ///@{
  1738 
  1739     /// \brief Checks if a node is reachable from the root(s).
  1740     ///
  1741     /// Returns \c true if \c v is reachable from the root(s).
  1742     /// \pre Either \ref run() or \ref start()
  1743     /// must be called before using this function.
  1744     bool reached(Node v) { return (*_reached)[v]; }
  1745 
  1746     ///@}
  1747 
  1748   };
  1749 
  1750 } //END OF NAMESPACE LEMON
  1751 
  1752 #endif