RhodeCode

    ///\retval reach Indicates if the target node is reached.

    ///It should be initially \c false.

    ///

    ///\return The processed node.

    ///

    ///\pre The queue must not be empty.

    Node processNextNode(Node target, bool& reach)

    {

      if(_queue_tail==_queue_next_dist) {

        _curr_dist++;

        _queue_next_dist=_queue_head;

      }

      Node n=_queue[_queue_tail++];

      _processed->set(n,true);

      Node m;

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

        if(!(*_reached)[m=G->target(e)]) {

          _queue[_queue_head++]=m;

          _reached->set(m,true);

          _pred->set(m,e);

          _dist->set(m,_curr_dist);

          reach = reach || (target == m);

        }

      return n;

    }

    ///Processes the next node.

    ///Processes the next node and checks if at least one of reached

    ///nodes has \c true value in the \c nm node map. If one node

    ///with \c true value is reachable from the processed node, then the

    ///\c rnode parameter will be set to the first of such nodes.

    ///

    ///\param nm A \c bool (or convertible) node map that indicates the

    ///possible targets.

    ///\retval rnode The reached target node.

    ///It should be initially \c INVALID.

    ///

    ///\return The processed node.

    ///

    ///\pre The queue must not be empty.

    template<class NM>

    Node processNextNode(const NM& nm, Node& rnode)

    {

      if(_queue_tail==_queue_next_dist) {

        _curr_dist++;

        _queue_next_dist=_queue_head;

      }

      Node n=_queue[_queue_tail++];

      _processed->set(n,true);

      Node m;

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

        if(!(*_reached)[m=G->target(e)]) {

          _queue[_queue_head++]=m;

          _reached->set(m,true);

          _pred->set(m,e);

          _dist->set(m,_curr_dist);

          if (nm[m] && rnode == INVALID) rnode = m;

        }

      return n;

    }

    ///The next node to be processed.

    ///Returns the next node to be processed or \c INVALID if the queue

    ///is empty.

    Node nextNode() const

    {

      return _queue_tail<_queue_head?_queue[_queue_tail]:INVALID;

    }

    ///\brief Returns \c false if there are nodes

    ///to be processed.

    ///

    ///Returns \c false if there are nodes

    ///to be processed in the queue.

    bool emptyQueue() const { return _queue_tail==_queue_head; }

    ///Returns the number of the nodes to be processed.

    ///Returns the number of the nodes to be processed in the queue.

    int queueSize() const { return _queue_head-_queue_tail; }

    ///Executes the algorithm.

    ///Executes the algorithm.

    ///

    ///This method runs the %BFS algorithm from the root node(s)

    ///in order to compute the shortest path to each node.

    ///

    ///The algorithm computes

    ///- the shortest path tree (forest),

    ///- the distance of each node from the root(s).

    ///

    ///\pre init() must be called and at least one root node should be

    ///added with addSource() before using this function.

    ///

    ///\note <tt>b.start()</tt> is just a shortcut of the following code.

    ///\code

    ///  while ( !b.emptyQueue() ) {

    ///    b.processNextNode();

    ///  }

    ///\endcode

    void start()

    {

      while ( !emptyQueue() ) processNextNode();

    }

    ///Executes the algorithm until the given target node is reached.

    ///Executes the algorithm until the given target node is reached.

    ///

    ///This method runs the %BFS algorithm from the root node(s)

    ///in order to compute the shortest path to \c dest.

    ///

    ///The algorithm computes

    ///- the shortest path to \c dest,

    ///- the distance of \c dest from the root(s).

    ///

    ///\pre init() must be called and at least one root node should be

    ///added with addSource() before using this function.

    ///

    ///\note <tt>b.start(t)</tt> is just a shortcut of the following code.

    ///\code

    ///  bool reach = false;

    ///  while ( !b.emptyQueue() && !reach ) {

    ///    b.processNextNode(t, reach);

    ///  }

    ///\endcode

    void start(Node dest)

    {

      bool reach = false;

      while ( !emptyQueue() && !reach ) processNextNode(dest, reach);

    }

    ///Executes the algorithm until a condition is met.

    ///Executes the algorithm until a condition is met.

    ///

    ///This method runs the %BFS algorithm from the root node(s) in

    ///order to compute the shortest path to a node \c v with

    /// <tt>nm[v]</tt> true, if such a node can be found.

    ///

    ///\param nm A \c bool (or convertible) node map. The algorithm

    ///will stop when it reaches a node \c v with <tt>nm[v]</tt> true.

    ///

    ///\return The reached node \c v with <tt>nm[v]</tt> true or

    ///\c INVALID if no such node was found.

    ///

    ///\pre init() must be called and at least one root node should be

    ///added with addSource() before using this function.

    ///

    ///\note <tt>b.start(nm)</tt> is just a shortcut of the following code.

    ///\code

    ///  Node rnode = INVALID;

    ///  while ( !b.emptyQueue() && rnode == INVALID ) {

    ///    b.processNextNode(nm, rnode);

    ///  }

    ///  return rnode;

    ///\endcode

    template<class NodeBoolMap>

    Node start(const NodeBoolMap &nm)

    {

      Node rnode = INVALID;

      while ( !emptyQueue() && rnode == INVALID ) {

        processNextNode(nm, rnode);

      }

      return rnode;

    }

    ///Runs the algorithm from the given node.

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

    ///in order to compute the shortest path to each node.

    ///

    ///The algorithm computes

    ///- the shortest path tree,

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

    ///

    ///\note <tt>b.run(s)</tt> is just a shortcut of the following code.

    ///\code

    ///  b.init();

    ///  b.addSource(s);

    ///  b.start();

    ///\endcode

    void run(Node s) {

      init();

      addSource(s);

      start();

    }

    ///Finds the shortest path between \c s and \c t.

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

    ///in order to compute the shortest path to \c t.

    ///

    ///\return The length of the shortest <tt>s</tt>--<tt>t</tt> path,

    ///if \c t is reachable form \c s, \c 0 otherwise.

    ///

    ///\note Apart from the return value, <tt>b.run(s,t)</tt> is just a

    ///shortcut of the following code.

    ///\code

    ///  b.init();

    ///  b.addSource(s);

    ///  b.start(t);

    ///\endcode

    int run(Node s,Node t) {

      init();

      addSource(s);

      start(t);

      return reached(t) ? _curr_dist : 0;

    }

    ///Runs the algorithm to visit all nodes in the digraph.

    ///This method runs the %BFS algorithm in order to

    ///compute the shortest path to each node.

    ///

    ///The algorithm computes

    ///- the shortest path tree (forest),

    ///- the distance of each node from the root(s).

    ///

    ///\note <tt>b.run(s)</tt> is just a shortcut of the following code.

    ///\code

    ///  b.init();

    ///  for (NodeIt n(gr); n != INVALID; ++n) {

    ///    if (!b.reached(n)) {

    ///      b.addSource(n);

    ///      b.start();

    ///    }

    ///  }

    ///\endcode

    void run() {

      init();

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

        if (!reached(n)) {

          addSource(n);

          start();

        }

      }

    }

    ///@}

    ///\name Query Functions

    ///The result of the %BFS algorithm can be obtained using these

    ///functions.\n

    ///Either \ref lemon::Bfs::run() "run()" or \ref lemon::Bfs::start()

    ///"start()" must be called before using them.

    ///@{

    ///The shortest path to a node.

    ///Returns the shortest path to a node.

    ///

    ///\warning \c t should be reachable from the root(s).

    ///

    ///\pre Either \ref run() or \ref start() must be called before

    ///using this function.

    Path path(Node t) const { return Path(*G, *_pred, t); }

    ///The distance of a node from the root(s).

    ///Returns the distance of a node from the root(s).

    ///

    ///\warning If node \c v is not reachable from the root(s), then

    ///the return value of this function is undefined.

    ///

    ///\pre Either \ref run() or \ref start() must be called before

    ///using this function.

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

    ///Returns the 'previous arc' of the shortest path tree for a node.

    ///This function returns the 'previous arc' of the shortest path

    ///tree for the node \c v, i.e. it returns the last arc of a

    ///shortest path from the root(s) to \c v. It is \c INVALID if \c v

    ///is not reachable from the root(s) or if \c v is a root.

    ///

    ///The shortest path tree used here is equal to the shortest path

    ///tree used in \ref predNode().

    ///

    ///\pre Either \ref run() or \ref start() must be called before

    ///using this function.

    Arc predArc(Node v) const { return (*_pred)[v];}

    ///Returns the 'previous node' of the shortest path tree for a node.

    ///This function returns the 'previous node' of the shortest path

    ///tree for the node \c v, i.e. it returns the last but one node

    ///from a shortest path from the root(s) to \c v. It is \c INVALID

    ///if \c v is not reachable from the root(s) or if \c v is a root.

    ///

    ///The shortest path tree used here is equal to the shortest path

    ///tree used in \ref predArc().

    ///

    ///\pre Either \ref run() or \ref start() must be called before

    ///using this function.

    Node predNode(Node v) const { return (*_pred)[v]==INVALID ? INVALID:

                                  G->source((*_pred)[v]); }

    ///\brief Returns a const reference to the node map that stores the

    /// distances of the nodes.

    ///

    ///Returns a const reference to the node map that stores the distances

    ///of the nodes calculated by the algorithm.

    ///

    ///\pre Either \ref run() or \ref init()

    ///must be called before using this function.

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

    ///\brief Returns a const reference to the node map that stores the

    ///predecessor arcs.

    ///

    ///Returns a const reference to the node map that stores the predecessor

    ///arcs, which form the shortest path tree.

    ///

    ///\pre Either \ref run() or \ref init()

    ///must be called before using this function.

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

    ///Checks if a node is reachable from the root(s).

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

    ///\pre Either \ref run() or \ref start()

    ///must be called before using this function.

    bool reached(Node v) const { return (*_reached)[v]; }

    ///@}

  };

  ///Default traits class of bfs() function.

  ///Default traits class of bfs() function.

  ///\tparam GR Digraph type.

  template<class GR>

  struct BfsWizardDefaultTraits

  {

    ///The type of the digraph the algorithm runs on.

    typedef GR Digraph;

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

    ///arcs of the shortest paths.

    ///

    ///The type of the map that stores the predecessor

    ///arcs of the shortest paths.

    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.

    typedef NullMap<typename Digraph::Node,typename Digraph::Arc> PredMap;

    ///Instantiates a \ref PredMap.

    ///This function instantiates a \ref PredMap.

    ///\param g is the digraph, to which we would like to define the

    ///\ref PredMap.

    ///\todo The digraph alone may be insufficient to initialize

#ifdef DOXYGEN

    static PredMap *createPredMap(const Digraph &g)

#else

    static PredMap *createPredMap(const Digraph &)

#endif

    {

      return new PredMap();

    }

    ///The type of the map that indicates which nodes are processed.

    ///The type of the map that indicates which nodes are processed.

    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.

    typedef NullMap<typename Digraph::Node,bool> ProcessedMap;

    ///Instantiates a \ref ProcessedMap.

    ///This function instantiates a \ref ProcessedMap.

    ///\param g is the digraph, to which

    ///we would like to define the \ref ProcessedMap.

#ifdef DOXYGEN

    static ProcessedMap *createProcessedMap(const Digraph &g)

#else

    static ProcessedMap *createProcessedMap(const Digraph &)

#endif

    {

      return new ProcessedMap();

    }

    ///The type of the map that indicates which nodes are reached.

    ///The type of the map that indicates which nodes are reached.

    ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.

    typedef typename Digraph::template NodeMap<bool> ReachedMap;

    ///Instantiates a \ref ReachedMap.

    ///This function instantiates a \ref ReachedMap.

    ///\param g is the digraph, to which

    ///we would like to define the \ref ReachedMap.

    static ReachedMap *createReachedMap(const Digraph &g)

    {

      return new ReachedMap(g);

    }

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

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

    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.

    ///

    typedef NullMap<typename Digraph::Node,int> DistMap;

    ///Instantiates a \ref DistMap.

    ///This function instantiates a \ref DistMap.

    ///\param g is the digraph, to which we would like to define

    ///the \ref DistMap

#ifdef DOXYGEN

    static DistMap *createDistMap(const Digraph &g)

#else

    static DistMap *createDistMap(const Digraph &)

#endif

    {

      return new DistMap();

    }

  };

  /// Default traits class used by \ref BfsWizard

  /// To make it easier to use Bfs algorithm

  /// we have created a wizard class.

  /// This \ref BfsWizard class needs default traits,

  /// as well as the \ref Bfs class.

  /// The \ref BfsWizardBase is a class to be the default traits of the

  /// \ref BfsWizard class.

  template<class GR>

  class BfsWizardBase : public BfsWizardDefaultTraits<GR>

  {

    typedef BfsWizardDefaultTraits<GR> Base;

  protected:

    //The type of the nodes in the digraph.

    typedef typename Base::Digraph::Node Node;

    //Pointer to the digraph the algorithm runs on.

    void *_g;

    //Pointer to the map of reached nodes.

    void *_reached;

    //Pointer to the map of processed nodes.

    void *_processed;

    //Pointer to the map of predecessors arcs.

    void *_pred;

    //Pointer to the map of distances.

    void *_dist;

    //Pointer to the source node.

    Node _source;

    public:

    /// Constructor.

    /// This constructor does not require parameters, therefore it initiates

    /// all of the attributes to default values (0, INVALID).

    BfsWizardBase() : _g(0), _reached(0), _processed(0), _pred(0),

                      _dist(0), _source(INVALID) {}

    /// Constructor.

    /// This constructor requires some parameters,

    /// listed in the parameters list.

    /// Others are initiated to 0.

    /// \param g The digraph the algorithm runs on.

    /// \param s The source node.

    BfsWizardBase(const GR &g, Node s=INVALID) :

      _g(reinterpret_cast<void*>(const_cast<GR*>(&g))),

      _reached(0), _processed(0), _pred(0), _dist(0), _source(s) {}

  };

  /// Auxiliary class for the function type interface of BFS algorithm.

  /// This auxiliary class is created to implement the function type

  /// interface of \ref Bfs algorithm. It uses the functions and features

  /// of the plain \ref Bfs, but it is much simpler to use it.

  /// It should only be used through the \ref bfs() function, which makes

  /// it easier to use the algorithm.

  ///

  /// Simplicity means that the way to change the types defined

  /// in the traits class is based on functions that returns the new class

  /// and not on templatable built-in classes.

  /// When using the plain \ref Bfs

  /// the new class with the modified type comes from

  /// the original class by using the ::

  /// operator. In the case of \ref BfsWizard only

  /// a function have to be called, and it will

  /// return the needed class.

  ///

  /// It does not have own \ref run() method. When its \ref run() method

  /// is called, it initiates a plain \ref Bfs object, and calls the

  /// \ref Bfs::run() method of it.

  template<class TR>

  class BfsWizard : public TR

  {

    typedef TR Base;

    ///The type of the digraph the algorithm runs on.

    typedef typename TR::Digraph Digraph;

    typedef typename Digraph::Node Node;

    typedef typename Digraph::NodeIt NodeIt;

    typedef typename Digraph::Arc Arc;

    typedef typename Digraph::OutArcIt OutArcIt;

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

    ///arcs of the shortest paths.

    typedef typename TR::PredMap PredMap;

    ///\brief The type of the map that stores the distances of the nodes.

    typedef typename TR::DistMap DistMap;

    ///\brief The type of the map that indicates which nodes are reached.

    typedef typename TR::ReachedMap ReachedMap;

    ///\brief The type of the map that indicates which nodes are processed.

    typedef typename TR::ProcessedMap ProcessedMap;

  public:

    /// Constructor.

    BfsWizard() : TR() {}

    /// Constructor that requires parameters.

    /// Constructor that requires parameters.

    /// These parameters will be the default values for the traits class.

    BfsWizard(const Digraph &g, Node s=INVALID) :

      TR(g,s) {}

    ///Copy constructor

    BfsWizard(const TR &b) : TR(b) {}

    ~BfsWizard() {}

    ///Runs BFS algorithm from a source node.

    ///Runs BFS algorithm from a source node.

    ///The node can be given with the \ref source() function.

    void run()

    {

      if(Base::_source==INVALID) throw UninitializedParameter();

      Bfs<Digraph,TR> alg(*reinterpret_cast<const Digraph*>(Base::_g));

      if(Base::_reached)

        alg.reachedMap(*reinterpret_cast<ReachedMap*>(Base::_reached));

      if(Base::_processed)

        alg.processedMap(*reinterpret_cast<ProcessedMap*>(Base::_processed));

      if(Base::_pred)

        alg.predMap(*reinterpret_cast<PredMap*>(Base::_pred));

      if(Base::_dist)

        alg.distMap(*reinterpret_cast<DistMap*>(Base::_dist));

      alg.run(Base::_source);

    }

    ///Runs BFS algorithm from the given node.

    ///Runs BFS algorithm from the given node.

    ///\param s is the given source.

    void run(Node s)

    {

      Base::_source=s;

      run();

    }

    /// Sets the source node, from which the Bfs algorithm runs.

    /// Sets the source node, from which the Bfs algorithm runs.

    /// \param s is the source node.

    BfsWizard<TR> &source(Node s)

    {

      Base::_source=s;

      return *this;

    }

    template<class T>

    struct DefPredMapBase : public Base {

      typedef T PredMap;

      static PredMap *createPredMap(const Digraph &) { return 0; };

      DefPredMapBase(const TR &b) : TR(b) {}

    };

    ///\brief \ref named-templ-param "Named parameter"

    ///for setting \ref PredMap object.

    ///

    /// \ref named-templ-param "Named parameter"

    ///for setting \ref PredMap object.

    template<class T>

    BfsWizard<DefPredMapBase<T> > predMap(const T &t)

    {

      Base::_pred=reinterpret_cast<void*>(const_cast<T*>(&t));

      return BfsWizard<DefPredMapBase<T> >(*this);

    }

    template<class T>

    struct DefReachedMapBase : public Base {

      typedef T ReachedMap;

      static ReachedMap *createReachedMap(const Digraph &) { return 0; };

      DefReachedMapBase(const TR &b) : TR(b) {}

    };

    ///\brief \ref named-templ-param "Named parameter"

    ///for setting \ref ReachedMap object.

    ///

    /// \ref named-templ-param "Named parameter"

    ///for setting \ref ReachedMap object.

    template<class T>

    BfsWizard<DefReachedMapBase<T> > reachedMap(const T &t)

    {

      Base::_reached=reinterpret_cast<void*>(const_cast<T*>(&t));

      return BfsWizard<DefReachedMapBase<T> >(*this);

    }

    template<class T>

    struct DefProcessedMapBase : public Base {

      typedef T ProcessedMap;

      static ProcessedMap *createProcessedMap(const Digraph &) { return 0; };

      DefProcessedMapBase(const TR &b) : TR(b) {}

    };

    ///\brief \ref named-templ-param "Named parameter"

    ///for setting \ref ProcessedMap object.

    ///

    /// \ref named-templ-param "Named parameter"

    ///for setting \ref ProcessedMap object.

    template<class T>

    BfsWizard<DefProcessedMapBase<T> > processedMap(const T &t)

    {

      Base::_processed=reinterpret_cast<void*>(const_cast<T*>(&t));

      return BfsWizard<DefProcessedMapBase<T> >(*this);

    }

    template<class T>

    struct DefDistMapBase : public Base {

      typedef T DistMap;

      static DistMap *createDistMap(const Digraph &) { return 0; };

      DefDistMapBase(const TR &b) : TR(b) {}

    };

    ///\brief \ref named-templ-param "Named parameter"

    ///for setting \ref DistMap object.

    ///

    /// \ref named-templ-param "Named parameter"

    ///for setting \ref DistMap object.

    template<class T>

    BfsWizard<DefDistMapBase<T> > distMap(const T &t)

    {

      Base::_dist=reinterpret_cast<void*>(const_cast<T*>(&t));

      return BfsWizard<DefDistMapBase<T> >(*this);

    }

  };

  ///Function type interface for Bfs algorithm.

  /// \ingroup search

  ///Function type interface for Bfs algorithm.

  ///

  ///This function also has several

  ///\ref named-templ-func-param "named parameters",

  ///they are declared as the members of class \ref BfsWizard.

  ///The following

  ///example shows how to use these parameters.

  ///\code

  ///  bfs(g,source).predMap(preds).run();

  ///\endcode

  ///\warning Don't forget to put the \ref BfsWizard::run() "run()"

  ///to the end of the parameter list.

  ///\sa BfsWizard

  ///\sa Bfs

  template<class GR>

  BfsWizard<BfsWizardBase<GR> >

  bfs(const GR &g,typename GR::Node s=INVALID)

  {

    return BfsWizard<BfsWizardBase<GR> >(g,s);

  }

#ifdef DOXYGEN

  /// \brief Visitor class for BFS.

  ///

  /// This class defines the interface of the BfsVisit events, and

  /// it could be the base of a real visitor class.

  template <typename _Digraph>

  struct BfsVisitor {

    typedef _Digraph Digraph;

    typedef typename Digraph::Arc Arc;

    typedef typename Digraph::Node Node;

    /// \brief Called for the source node(s) of the BFS.

    ///

    /// This function is called for the source node(s) of the BFS.

    void start(const Node& node) {}

    /// \brief Called when a node is reached first time.

    ///

    /// This function is called when a node is reached first time.

    void reach(const Node& node) {}

    /// \brief Called when a node is processed.

    ///

    /// This function is called when a node is processed.

    void process(const Node& node) {}

    /// \brief Called when an arc reaches a new node.

    ///

    /// This function is called when the BFS finds an arc whose target node

    /// is not reached yet.

    void discover(const Arc& arc) {}

    /// \brief Called when an arc is examined but its target node is

    /// already discovered.

    ///

    /// This function is called when an arc is examined but its target node is

    /// already discovered.

    void examine(const Arc& arc) {}

  };

#else

  template <typename _Digraph>

  struct BfsVisitor {

    typedef _Digraph Digraph;

    typedef typename Digraph::Arc Arc;

    typedef typename Digraph::Node Node;

    void start(const Node&) {}

    void reach(const Node&) {}

    void process(const Node&) {}

    void discover(const Arc&) {}

    void examine(const Arc&) {}

    template <typename _Visitor>

    struct Constraints {

      void constraints() {

        Arc arc;

        Node node;

        visitor.start(node);

        visitor.reach(node);

        visitor.process(node);

        visitor.discover(arc);

        visitor.examine(arc);

      }

      _Visitor& visitor;

    };

  };

#endif

  /// \brief Default traits class of BfsVisit class.

  ///

  /// Default traits class of BfsVisit class.

  /// \tparam _Digraph The type of the digraph the algorithm runs on.

  template<class _Digraph>

  struct BfsVisitDefaultTraits {

    /// \brief The type of the digraph the algorithm runs on.

    typedef _Digraph Digraph;

    /// \brief The type of the map that indicates which nodes are reached.

    ///

    /// The type of the map that indicates which nodes are reached.

    /// It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.

    typedef typename Digraph::template NodeMap<bool> ReachedMap;

    /// \brief Instantiates a \ref ReachedMap.

    ///

    /// This function instantiates a \ref ReachedMap.

    /// \param digraph is the digraph, to which

    /// we would like to define the \ref ReachedMap.

    static ReachedMap *createReachedMap(const Digraph &digraph) {

      return new ReachedMap(digraph);

    }

  };

  /// \ingroup search

  ///

  /// \brief %BFS algorithm class with visitor interface.

  ///

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

  /// with visitor interface.

  ///

  /// The %BfsVisit class provides an alternative interface to the Bfs

  /// class. It works with callback mechanism, the BfsVisit object calls

  /// the member functions of the \c Visitor class on every BFS event.

  ///

  /// \tparam _Digraph The type of the digraph the algorithm runs on.

  /// The default value is

  /// \ref ListDigraph. The value of _Digraph is not used directly by

  /// \ref BfsVisit, it is only passed to \ref BfsVisitDefaultTraits.

  /// \tparam _Visitor The Visitor type that is used by the algorithm.

  /// \ref BfsVisitor "BfsVisitor<_Digraph>" is an empty visitor, which

  /// does not observe the BFS events. If you want to observe the BFS

  /// events, you should implement your own visitor class.

  /// \tparam _Traits Traits class to set various data types used by the

  /// algorithm. The default traits class is

  /// \ref BfsVisitDefaultTraits "BfsVisitDefaultTraits<_Digraph>".

  /// See \ref BfsVisitDefaultTraits for the documentation of

  /// a BFS visit traits class.

#ifdef DOXYGEN

  template <typename _Digraph, typename _Visitor, typename _Traits>

#else

  template <typename _Digraph = ListDigraph,

            typename _Visitor = BfsVisitor<_Digraph>,

            typename _Traits = BfsDefaultTraits<_Digraph> >

#endif

  class BfsVisit {

  public:

    /// \brief \ref Exception for uninitialized parameters.

    ///

    /// This error represents problems in the initialization

    /// of the parameters of the algorithm.

    class UninitializedParameter : public lemon::UninitializedParameter {

    public:

      virtual const char* what() const throw()

      {

        return "lemon::BfsVisit::UninitializedParameter";

      }

    };

    ///The traits class.

    typedef _Traits Traits;

    ///The type of the digraph the algorithm runs on.

    typedef typename Traits::Digraph Digraph;

    ///The visitor type used by the algorithm.

    typedef _Visitor Visitor;

    ///The type of the map that indicates which nodes are reached.

    typedef typename Traits::ReachedMap ReachedMap;

  private:

    typedef typename Digraph::Node Node;

    typedef typename Digraph::NodeIt NodeIt;

    typedef typename Digraph::Arc Arc;

    typedef typename Digraph::OutArcIt OutArcIt;

    //Pointer to the underlying digraph.

    const Digraph *_digraph;

    //Pointer to the visitor object.

    Visitor *_visitor;

    //Pointer to the map of reached status of the nodes.

    ReachedMap *_reached;

    //Indicates if _reached is locally allocated (true) or not.

    bool local_reached;

    std::vector<typename Digraph::Node> _list;

    int _list_front, _list_back;

    ///Creates the maps if necessary.

    ///\todo Better memory allocation (instead of new).

    void create_maps() {

      if(!_reached) {

        local_reached = true;

        _reached = Traits::createReachedMap(*_digraph);

      }

    }

  protected:

    BfsVisit() {}

  public:

    typedef BfsVisit Create;

    /// \name Named template parameters

    ///@{

    template <class T>

    struct DefReachedMapTraits : public Traits {

      typedef T ReachedMap;

      static ReachedMap *createReachedMap(const Digraph &digraph) {

        throw UninitializedParameter();

      }

    };

    /// \brief \ref named-templ-param "Named parameter" for setting

    /// ReachedMap type.

    ///

    /// \ref named-templ-param "Named parameter" for setting ReachedMap type.

    template <class T>

    struct DefReachedMap : public BfsVisit< Digraph, Visitor,

                                            DefReachedMapTraits<T> > {

      typedef BfsVisit< Digraph, Visitor, DefReachedMapTraits<T> > Create;

    };

    ///@}

  public:

    /// \brief Constructor.

    ///

    /// Constructor.

    ///

    /// \param digraph The digraph the algorithm runs on.

    /// \param visitor The visitor object of the algorithm.

    BfsVisit(const Digraph& digraph, Visitor& visitor)

      : _digraph(&digraph), _visitor(&visitor),

        _reached(0), local_reached(false) {}

    /// \brief Destructor.

    ~BfsVisit() {

      if(local_reached) delete _reached;

    }

    /// \brief Sets the map that indicates which nodes are reached.

    ///

    /// Sets the map that indicates which nodes are reached.

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

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

    /// automatically allocated map, of course.

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

    BfsVisit &reachedMap(ReachedMap &m) {

      if(local_reached) {

        delete _reached;

        local_reached = false;

      }

      _reached = &m;

      return *this;

    }

  public:

    /// \name Execution control

    /// The simplest way to execute the algorithm is to use

    /// one of the member functions called \ref lemon::BfsVisit::run()

    /// "run()".

    /// \n

    /// If you need more control on the execution, first you must call

    /// \ref lemon::BfsVisit::init() "init()", then you can add several

    /// source nodes with \ref lemon::BfsVisit::addSource() "addSource()".

    /// Finally \ref lemon::BfsVisit::start() "start()" will perform the

    /// actual path computation.

    /// @{

    /// \brief Initializes the internal data structures.

    ///

    /// Initializes the internal data structures.

    void init() {

      create_maps();

      _list.resize(countNodes(*_digraph));

      _list_front = _list_back = -1;

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

        _reached->set(u, false);

      }

    }

    /// \brief Adds a new source node.

    ///

    /// Adds a new source node to the set of nodes to be processed.

    void addSource(Node s) {

      if(!(*_reached)[s]) {

          _reached->set(s,true);

          _visitor->start(s);

          _visitor->reach(s);

          _list[++_list_back] = s;

        }

    }

    /// \brief Processes the next node.

    ///

    /// Processes the next node.

    ///

    /// \return The processed node.

    ///

    /// \pre The queue must not be empty.

    Node processNextNode() {

      Node n = _list[++_list_front];

      _visitor->process(n);

      Arc e;

      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {

        Node m = _digraph->target(e);

        if (!(*_reached)[m]) {

          _visitor->discover(e);

          _visitor->reach(m);

          _reached->set(m, true);

          _list[++_list_back] = m;

        } else {

          _visitor->examine(e);

        }

      }

      return n;

    }

    /// \brief Processes the next node.

    ///

    /// Processes the next node and checks if the given target node

    /// is reached. If the target node is reachable from the processed

    /// node, then the \c reach parameter will be set to \c true.

    ///

    /// \param target The target node.

    /// \retval reach Indicates if the target node is reached.

    /// It should be initially \c false.

    ///

    /// \return The processed node.

    ///

    /// \pre The queue must not be empty.

    Node processNextNode(Node target, bool& reach) {

      Node n = _list[++_list_front];

      _visitor->process(n);

      Arc e;

      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {

        Node m = _digraph->target(e);

        if (!(*_reached)[m]) {

          _visitor->discover(e);

          _visitor->reach(m);

          _reached->set(m, true);

          _list[++_list_back] = m;

          reach = reach || (target == m);

        } else {

          _visitor->examine(e);

        }

      }

      return n;

    }

    /// \brief Processes the next node.

    ///

    /// Processes the next node and checks if at least one of reached

    /// nodes has \c true value in the \c nm node map. If one node

    /// with \c true value is reachable from the processed node, then the

    /// \c rnode parameter will be set to the first of such nodes.

    ///

    /// \param nm A \c bool (or convertible) node map that indicates the

    /// possible targets.

    /// \retval rnode The reached target node.

    /// It should be initially \c INVALID.

    ///

    /// \return The processed node.

    ///

    /// \pre The queue must not be empty.

    template <typename NM>

    Node processNextNode(const NM& nm, Node& rnode) {

      Node n = _list[++_list_front];

      _visitor->process(n);

      Arc e;

      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {

        Node m = _digraph->target(e);

        if (!(*_reached)[m]) {

          _visitor->discover(e);

          _visitor->reach(m);

          _reached->set(m, true);

          _list[++_list_back] = m;

          if (nm[m] && rnode == INVALID) rnode = m;

        } else {

          _visitor->examine(e);

        }

      }

      return n;

    }

    /// \brief The next node to be processed.

    ///

    /// Returns the next node to be processed or \c INVALID if the queue

    /// is empty.

    Node nextNode() const {

      return _list_front != _list_back ? _list[_list_front + 1] : INVALID;

    }

    /// \brief Returns \c false if there are nodes

    /// to be processed.

    ///

    /// Returns \c false if there are nodes

    /// to be processed in the queue.

    bool emptyQueue() const { return _list_front == _list_back; }

    /// \brief Returns the number of the nodes to be processed.

    ///

    /// Returns the number of the nodes to be processed in the queue.

    int queueSize() const { return _list_back - _list_front; }

    /// \brief Executes the algorithm.

    ///

    /// Executes the algorithm.

    ///

    /// This method runs the %BFS algorithm from the root node(s)

    /// in order to compute the shortest path to each node.

    ///

    /// The algorithm computes

    /// - the shortest path tree (forest),

    /// - the distance of each node from the root(s).

    ///

    /// \pre init() must be called and at least one root node should be added

    /// with addSource() before using this function.

    ///

    /// \note <tt>b.start()</tt> is just a shortcut of the following code.

    /// \code

    ///   while ( !b.emptyQueue() ) {

    ///     b.processNextNode();

    ///   }

    /// \endcode

    void start() {

      while ( !emptyQueue() ) processNextNode();

    }

    /// \brief Executes the algorithm until the given target node is reached.

    ///

    /// Executes the algorithm until the given target node is reached.

    ///

    /// This method runs the %BFS algorithm from the root node(s)

    /// in order to compute the shortest path to \c dest.

    ///

    /// The algorithm computes

    /// - the shortest path to \c dest,

    /// - the distance of \c dest from the root(s).

    ///

    /// \pre init() must be called and at least one root node should be

    /// added with addSource() before using this function.

    ///

    /// \note <tt>b.start(t)</tt> is just a shortcut of the following code.

    /// \code

    ///   bool reach = false;

    ///   while ( !b.emptyQueue() && !reach ) {

    ///     b.processNextNode(t, reach);

    ///   }

    /// \endcode

    void start(Node dest) {

      bool reach = false;

      while ( !emptyQueue() && !reach ) processNextNode(dest, reach);

    }

    /// \brief Executes the algorithm until a condition is met.

    ///

    /// Executes the algorithm until a condition is met.

    ///

    /// This method runs the %BFS algorithm from the root node(s) in

    /// order to compute the shortest path to a node \c v with