COIN-OR::LEMON - Graph Library

source: lemon-1.0/lemon/bfs.h @ 280:e7f8647ce760

Last change on this file since 280:e7f8647ce760 was 280:e7f8647ce760, checked in by Alpar Juttner <alpar@…>, 11 years ago

Remove todo-s and convert them to trac tickets

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