COIN-OR::LEMON - Graph Library

source: lemon/lemon/bfs.h @ 463:88ed40ad0d4f

Last change on this file since 463:88ed40ad0d4f was 463:88ed40ad0d4f, checked in by Alpar Juttner <alpar@…>, 11 years ago

Happy New Year again

  • update the copyright headers + run the source unifier
File size: 54.3 KB
Line 
1/* -*- mode: C++; indent-tabs-mode: nil; -*-
2 *
3 * This file is a part of LEMON, a generic C++ optimization library.
4 *
5 * Copyright (C) 2003-2009
6 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
7 * (Egervary Research Group on Combinatorial Optimization, EGRES).
8 *
9 * Permission to use, modify and distribute this software is granted
10 * provided that this copyright notice appears in all copies. For
11 * precise terms see the accompanying LICENSE file.
12 *
13 * This software is provided "AS IS" with no warranty of any kind,
14 * express or implied, and with no claim as to its suitability for any
15 * purpose.
16 *
17 */
18
19#ifndef LEMON_BFS_H
20#define LEMON_BFS_H
21
22///\ingroup search
23///\file
24///\brief BFS algorithm.
25
26#include <lemon/list_graph.h>
27#include <lemon/bits/path_dump.h>
28#include <lemon/core.h>
29#include <lemon/error.h>
30#include <lemon/maps.h>
31#include <lemon/path.h>
32
33namespace lemon {
34
35  ///Default traits class of Bfs class.
36
37  ///Default traits class of Bfs class.
38  ///\tparam GR Digraph type.
39  template<class GR>
40  struct BfsDefaultTraits
41  {
42    ///The type of the digraph the algorithm runs on.
43    typedef GR Digraph;
44
45    ///\brief The type of the map that stores the predecessor
46    ///arcs of the shortest paths.
47    ///
48    ///The type of the map that stores the predecessor
49    ///arcs of the shortest paths.
50    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
51    typedef typename Digraph::template NodeMap<typename Digraph::Arc> PredMap;
52    ///Instantiates a PredMap.
53
54    ///This function instantiates a PredMap.
55    ///\param g is the digraph, to which we would like to define the
56    ///PredMap.
57    static PredMap *createPredMap(const Digraph &g)
58    {
59      return new PredMap(g);
60    }
61
62    ///The type of the map that indicates which nodes are processed.
63
64    ///The type of the map that indicates which nodes are processed.
65    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
66    typedef NullMap<typename Digraph::Node,bool> ProcessedMap;
67    ///Instantiates a ProcessedMap.
68
69    ///This function instantiates a ProcessedMap.
70    ///\param g is the digraph, to which
71    ///we would like to define the ProcessedMap
72#ifdef DOXYGEN
73    static ProcessedMap *createProcessedMap(const Digraph &g)
74#else
75    static ProcessedMap *createProcessedMap(const Digraph &)
76#endif
77    {
78      return new ProcessedMap();
79    }
80
81    ///The type of the map that indicates which nodes are reached.
82
83    ///The type of the map that indicates which nodes are reached.
84    ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
85    typedef typename Digraph::template NodeMap<bool> ReachedMap;
86    ///Instantiates a ReachedMap.
87
88    ///This function instantiates a ReachedMap.
89    ///\param g is the digraph, to which
90    ///we would like to define the ReachedMap.
91    static ReachedMap *createReachedMap(const Digraph &g)
92    {
93      return new ReachedMap(g);
94    }
95
96    ///The type of the map that stores the distances of the nodes.
97
98    ///The type of the map that stores the distances of the nodes.
99    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
100    typedef typename Digraph::template NodeMap<int> DistMap;
101    ///Instantiates a DistMap.
102
103    ///This function instantiates a DistMap.
104    ///\param g is the digraph, to which we would like to define the
105    ///DistMap.
106    static DistMap *createDistMap(const Digraph &g)
107    {
108      return new DistMap(g);
109    }
110  };
111
112  ///%BFS algorithm class.
113
114  ///\ingroup search
115  ///This class provides an efficient implementation of the %BFS algorithm.
116  ///
117  ///There is also a \ref bfs() "function-type interface" for the BFS
118  ///algorithm, which is convenient in the simplier cases and it can be
119  ///used easier.
120  ///
121  ///\tparam GR The type of the digraph the algorithm runs on.
122  ///The default type is \ref ListDigraph.
123#ifdef DOXYGEN
124  template <typename GR,
125            typename TR>
126#else
127  template <typename GR=ListDigraph,
128            typename TR=BfsDefaultTraits<GR> >
129#endif
130  class Bfs {
131  public:
132
133    ///The type of the digraph the algorithm runs on.
134    typedef typename TR::Digraph Digraph;
135
136    ///\brief The type of the map that stores the predecessor arcs of the
137    ///shortest paths.
138    typedef typename TR::PredMap PredMap;
139    ///The type of the map that stores the distances of the nodes.
140    typedef typename TR::DistMap DistMap;
141    ///The type of the map that indicates which nodes are reached.
142    typedef typename TR::ReachedMap ReachedMap;
143    ///The type of the map that indicates which nodes are processed.
144    typedef typename TR::ProcessedMap ProcessedMap;
145    ///The type of the paths.
146    typedef PredMapPath<Digraph, PredMap> Path;
147
148    ///The \ref BfsDefaultTraits "traits class" of the algorithm.
149    typedef TR Traits;
150
151  private:
152
153    typedef typename Digraph::Node Node;
154    typedef typename Digraph::NodeIt NodeIt;
155    typedef typename Digraph::Arc Arc;
156    typedef typename Digraph::OutArcIt OutArcIt;
157
158    //Pointer to the underlying digraph.
159    const Digraph *G;
160    //Pointer to the map of predecessor arcs.
161    PredMap *_pred;
162    //Indicates if _pred is locally allocated (true) or not.
163    bool local_pred;
164    //Pointer to the map of distances.
165    DistMap *_dist;
166    //Indicates if _dist is locally allocated (true) or not.
167    bool local_dist;
168    //Pointer to the map of reached status of the nodes.
169    ReachedMap *_reached;
170    //Indicates if _reached is locally allocated (true) or not.
171    bool local_reached;
172    //Pointer to the map of processed status of the nodes.
173    ProcessedMap *_processed;
174    //Indicates if _processed is locally allocated (true) or not.
175    bool local_processed;
176
177    std::vector<typename Digraph::Node> _queue;
178    int _queue_head,_queue_tail,_queue_next_dist;
179    int _curr_dist;
180
181    //Creates the maps if necessary.
182    void create_maps()
183    {
184      if(!_pred) {
185        local_pred = true;
186        _pred = Traits::createPredMap(*G);
187      }
188      if(!_dist) {
189        local_dist = true;
190        _dist = Traits::createDistMap(*G);
191      }
192      if(!_reached) {
193        local_reached = true;
194        _reached = Traits::createReachedMap(*G);
195      }
196      if(!_processed) {
197        local_processed = true;
198        _processed = Traits::createProcessedMap(*G);
199      }
200    }
201
202  protected:
203
204    Bfs() {}
205
206  public:
207
208    typedef Bfs Create;
209
210    ///\name Named Template Parameters
211
212    ///@{
213
214    template <class T>
215    struct SetPredMapTraits : public Traits {
216      typedef T PredMap;
217      static PredMap *createPredMap(const Digraph &)
218      {
219        LEMON_ASSERT(false, "PredMap is not initialized");
220        return 0; // ignore warnings
221      }
222    };
223    ///\brief \ref named-templ-param "Named parameter" for setting
224    ///PredMap type.
225    ///
226    ///\ref named-templ-param "Named parameter" for setting
227    ///PredMap type.
228    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
229    template <class T>
230    struct SetPredMap : public Bfs< Digraph, SetPredMapTraits<T> > {
231      typedef Bfs< Digraph, SetPredMapTraits<T> > Create;
232    };
233
234    template <class T>
235    struct SetDistMapTraits : public Traits {
236      typedef T DistMap;
237      static DistMap *createDistMap(const Digraph &)
238      {
239        LEMON_ASSERT(false, "DistMap is not initialized");
240        return 0; // ignore warnings
241      }
242    };
243    ///\brief \ref named-templ-param "Named parameter" for setting
244    ///DistMap type.
245    ///
246    ///\ref named-templ-param "Named parameter" for setting
247    ///DistMap type.
248    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
249    template <class T>
250    struct SetDistMap : public Bfs< Digraph, SetDistMapTraits<T> > {
251      typedef Bfs< Digraph, SetDistMapTraits<T> > Create;
252    };
253
254    template <class T>
255    struct SetReachedMapTraits : public Traits {
256      typedef T ReachedMap;
257      static ReachedMap *createReachedMap(const Digraph &)
258      {
259        LEMON_ASSERT(false, "ReachedMap is not initialized");
260        return 0; // ignore warnings
261      }
262    };
263    ///\brief \ref named-templ-param "Named parameter" for setting
264    ///ReachedMap type.
265    ///
266    ///\ref named-templ-param "Named parameter" for setting
267    ///ReachedMap type.
268    ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
269    template <class T>
270    struct SetReachedMap : public Bfs< Digraph, SetReachedMapTraits<T> > {
271      typedef Bfs< Digraph, SetReachedMapTraits<T> > Create;
272    };
273
274    template <class T>
275    struct SetProcessedMapTraits : public Traits {
276      typedef T ProcessedMap;
277      static ProcessedMap *createProcessedMap(const Digraph &)
278      {
279        LEMON_ASSERT(false, "ProcessedMap is not initialized");
280        return 0; // ignore warnings
281      }
282    };
283    ///\brief \ref named-templ-param "Named parameter" for setting
284    ///ProcessedMap type.
285    ///
286    ///\ref named-templ-param "Named parameter" for setting
287    ///ProcessedMap type.
288    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
289    template <class T>
290    struct SetProcessedMap : public Bfs< Digraph, SetProcessedMapTraits<T> > {
291      typedef Bfs< Digraph, SetProcessedMapTraits<T> > Create;
292    };
293
294    struct SetStandardProcessedMapTraits : public Traits {
295      typedef typename Digraph::template NodeMap<bool> ProcessedMap;
296      static ProcessedMap *createProcessedMap(const Digraph &g)
297      {
298        return new ProcessedMap(g);
299        return 0; // ignore warnings
300      }
301    };
302    ///\brief \ref named-templ-param "Named parameter" for setting
303    ///ProcessedMap type to be <tt>Digraph::NodeMap<bool></tt>.
304    ///
305    ///\ref named-templ-param "Named parameter" for setting
306    ///ProcessedMap type to be <tt>Digraph::NodeMap<bool></tt>.
307    ///If you don't set it explicitly, it will be automatically allocated.
308    struct SetStandardProcessedMap :
309      public Bfs< Digraph, SetStandardProcessedMapTraits > {
310      typedef Bfs< Digraph, SetStandardProcessedMapTraits > Create;
311    };
312
313    ///@}
314
315  public:
316
317    ///Constructor.
318
319    ///Constructor.
320    ///\param g The digraph the algorithm runs on.
321    Bfs(const Digraph &g) :
322      G(&g),
323      _pred(NULL), local_pred(false),
324      _dist(NULL), local_dist(false),
325      _reached(NULL), local_reached(false),
326      _processed(NULL), local_processed(false)
327    { }
328
329    ///Destructor.
330    ~Bfs()
331    {
332      if(local_pred) delete _pred;
333      if(local_dist) delete _dist;
334      if(local_reached) delete _reached;
335      if(local_processed) delete _processed;
336    }
337
338    ///Sets the map that stores the predecessor arcs.
339
340    ///Sets the map that stores the predecessor arcs.
341    ///If you don't use this function before calling \ref run(Node) "run()"
342    ///or \ref init(), an instance will be allocated automatically.
343    ///The destructor deallocates this automatically allocated map,
344    ///of course.
345    ///\return <tt> (*this) </tt>
346    Bfs &predMap(PredMap &m)
347    {
348      if(local_pred) {
349        delete _pred;
350        local_pred=false;
351      }
352      _pred = &m;
353      return *this;
354    }
355
356    ///Sets the map that indicates which nodes are reached.
357
358    ///Sets the map that indicates which nodes are reached.
359    ///If you don't use this function before calling \ref run(Node) "run()"
360    ///or \ref init(), an instance will be allocated automatically.
361    ///The destructor deallocates this automatically allocated map,
362    ///of course.
363    ///\return <tt> (*this) </tt>
364    Bfs &reachedMap(ReachedMap &m)
365    {
366      if(local_reached) {
367        delete _reached;
368        local_reached=false;
369      }
370      _reached = &m;
371      return *this;
372    }
373
374    ///Sets the map that indicates which nodes are processed.
375
376    ///Sets the map that indicates which nodes are processed.
377    ///If you don't use this function before calling \ref run(Node) "run()"
378    ///or \ref init(), an instance will be allocated automatically.
379    ///The destructor deallocates this automatically allocated map,
380    ///of course.
381    ///\return <tt> (*this) </tt>
382    Bfs &processedMap(ProcessedMap &m)
383    {
384      if(local_processed) {
385        delete _processed;
386        local_processed=false;
387      }
388      _processed = &m;
389      return *this;
390    }
391
392    ///Sets the map that stores the distances of the nodes.
393
394    ///Sets the map that stores the distances of the nodes calculated by
395    ///the algorithm.
396    ///If you don't use this function before calling \ref run(Node) "run()"
397    ///or \ref init(), an instance will be allocated automatically.
398    ///The destructor deallocates this automatically allocated map,
399    ///of course.
400    ///\return <tt> (*this) </tt>
401    Bfs &distMap(DistMap &m)
402    {
403      if(local_dist) {
404        delete _dist;
405        local_dist=false;
406      }
407      _dist = &m;
408      return *this;
409    }
410
411  public:
412
413    ///\name Execution Control
414    ///The simplest way to execute the BFS algorithm is to use one of the
415    ///member functions called \ref run(Node) "run()".\n
416    ///If you need more control on the execution, first you have to call
417    ///\ref init(), then you can add several source nodes with
418    ///\ref addSource(). Finally the actual path computation can be
419    ///performed with one of the \ref start() functions.
420
421    ///@{
422
423    ///\brief Initializes the internal data structures.
424    ///
425    ///Initializes the internal data structures.
426    void init()
427    {
428      create_maps();
429      _queue.resize(countNodes(*G));
430      _queue_head=_queue_tail=0;
431      _curr_dist=1;
432      for ( NodeIt u(*G) ; u!=INVALID ; ++u ) {
433        _pred->set(u,INVALID);
434        _reached->set(u,false);
435        _processed->set(u,false);
436      }
437    }
438
439    ///Adds a new source node.
440
441    ///Adds a new source node to the set of nodes to be processed.
442    ///
443    void addSource(Node s)
444    {
445      if(!(*_reached)[s])
446        {
447          _reached->set(s,true);
448          _pred->set(s,INVALID);
449          _dist->set(s,0);
450          _queue[_queue_head++]=s;
451          _queue_next_dist=_queue_head;
452        }
453    }
454
455    ///Processes the next node.
456
457    ///Processes the next node.
458    ///
459    ///\return The processed node.
460    ///
461    ///\pre The queue must not be empty.
462    Node processNextNode()
463    {
464      if(_queue_tail==_queue_next_dist) {
465        _curr_dist++;
466        _queue_next_dist=_queue_head;
467      }
468      Node n=_queue[_queue_tail++];
469      _processed->set(n,true);
470      Node m;
471      for(OutArcIt e(*G,n);e!=INVALID;++e)
472        if(!(*_reached)[m=G->target(e)]) {
473          _queue[_queue_head++]=m;
474          _reached->set(m,true);
475          _pred->set(m,e);
476          _dist->set(m,_curr_dist);
477        }
478      return n;
479    }
480
481    ///Processes the next node.
482
483    ///Processes the next node and checks if the given target node
484    ///is reached. If the target node is reachable from the processed
485    ///node, then the \c reach parameter will be set to \c true.
486    ///
487    ///\param target The target node.
488    ///\retval reach Indicates if the target node is reached.
489    ///It should be initially \c false.
490    ///
491    ///\return The processed node.
492    ///
493    ///\pre The queue must not be empty.
494    Node processNextNode(Node target, bool& reach)
495    {
496      if(_queue_tail==_queue_next_dist) {
497        _curr_dist++;
498        _queue_next_dist=_queue_head;
499      }
500      Node n=_queue[_queue_tail++];
501      _processed->set(n,true);
502      Node m;
503      for(OutArcIt e(*G,n);e!=INVALID;++e)
504        if(!(*_reached)[m=G->target(e)]) {
505          _queue[_queue_head++]=m;
506          _reached->set(m,true);
507          _pred->set(m,e);
508          _dist->set(m,_curr_dist);
509          reach = reach || (target == m);
510        }
511      return n;
512    }
513
514    ///Processes the next node.
515
516    ///Processes the next node and checks if at least one of reached
517    ///nodes has \c true value in the \c nm node map. If one node
518    ///with \c true value is reachable from the processed node, then the
519    ///\c rnode parameter will be set to the first of such nodes.
520    ///
521    ///\param nm A \c bool (or convertible) node map that indicates the
522    ///possible targets.
523    ///\retval rnode The reached target node.
524    ///It should be initially \c INVALID.
525    ///
526    ///\return The processed node.
527    ///
528    ///\pre The queue must not be empty.
529    template<class NM>
530    Node processNextNode(const NM& nm, Node& rnode)
531    {
532      if(_queue_tail==_queue_next_dist) {
533        _curr_dist++;
534        _queue_next_dist=_queue_head;
535      }
536      Node n=_queue[_queue_tail++];
537      _processed->set(n,true);
538      Node m;
539      for(OutArcIt e(*G,n);e!=INVALID;++e)
540        if(!(*_reached)[m=G->target(e)]) {
541          _queue[_queue_head++]=m;
542          _reached->set(m,true);
543          _pred->set(m,e);
544          _dist->set(m,_curr_dist);
545          if (nm[m] && rnode == INVALID) rnode = m;
546        }
547      return n;
548    }
549
550    ///The next node to be processed.
551
552    ///Returns the next node to be processed or \c INVALID if the queue
553    ///is empty.
554    Node nextNode() const
555    {
556      return _queue_tail<_queue_head?_queue[_queue_tail]:INVALID;
557    }
558
559    ///Returns \c false if there are nodes to be processed.
560
561    ///Returns \c false if there are nodes to be processed
562    ///in the queue.
563    bool emptyQueue() const { return _queue_tail==_queue_head; }
564
565    ///Returns the number of the nodes to be processed.
566
567    ///Returns the number of the nodes to be processed
568    ///in the queue.
569    int queueSize() const { return _queue_head-_queue_tail; }
570
571    ///Executes the algorithm.
572
573    ///Executes the algorithm.
574    ///
575    ///This method runs the %BFS algorithm from the root node(s)
576    ///in order to compute the shortest path to each node.
577    ///
578    ///The algorithm computes
579    ///- the shortest path tree (forest),
580    ///- the distance of each node from the root(s).
581    ///
582    ///\pre init() must be called and at least one root node should be
583    ///added with addSource() before using this function.
584    ///
585    ///\note <tt>b.start()</tt> is just a shortcut of the following code.
586    ///\code
587    ///  while ( !b.emptyQueue() ) {
588    ///    b.processNextNode();
589    ///  }
590    ///\endcode
591    void start()
592    {
593      while ( !emptyQueue() ) processNextNode();
594    }
595
596    ///Executes the algorithm until the given target node is reached.
597
598    ///Executes the algorithm until the given target node is reached.
599    ///
600    ///This method runs the %BFS algorithm from the root node(s)
601    ///in order to compute the shortest path to \c t.
602    ///
603    ///The algorithm computes
604    ///- the shortest path to \c t,
605    ///- the distance of \c t from the root(s).
606    ///
607    ///\pre init() must be called and at least one root node should be
608    ///added with addSource() before using this function.
609    ///
610    ///\note <tt>b.start(t)</tt> is just a shortcut of the following code.
611    ///\code
612    ///  bool reach = false;
613    ///  while ( !b.emptyQueue() && !reach ) {
614    ///    b.processNextNode(t, reach);
615    ///  }
616    ///\endcode
617    void start(Node t)
618    {
619      bool reach = false;
620      while ( !emptyQueue() && !reach ) processNextNode(t, reach);
621    }
622
623    ///Executes the algorithm until a condition is met.
624
625    ///Executes the algorithm until a condition is met.
626    ///
627    ///This method runs the %BFS algorithm from the root node(s) in
628    ///order to compute the shortest path to a node \c v with
629    /// <tt>nm[v]</tt> true, if such a node can be found.
630    ///
631    ///\param nm A \c bool (or convertible) node map. The algorithm
632    ///will stop when it reaches a node \c v with <tt>nm[v]</tt> true.
633    ///
634    ///\return The reached node \c v with <tt>nm[v]</tt> true or
635    ///\c INVALID if no such node was found.
636    ///
637    ///\pre init() must be called and at least one root node should be
638    ///added with addSource() before using this function.
639    ///
640    ///\note <tt>b.start(nm)</tt> is just a shortcut of the following code.
641    ///\code
642    ///  Node rnode = INVALID;
643    ///  while ( !b.emptyQueue() && rnode == INVALID ) {
644    ///    b.processNextNode(nm, rnode);
645    ///  }
646    ///  return rnode;
647    ///\endcode
648    template<class NodeBoolMap>
649    Node start(const NodeBoolMap &nm)
650    {
651      Node rnode = INVALID;
652      while ( !emptyQueue() && rnode == INVALID ) {
653        processNextNode(nm, rnode);
654      }
655      return rnode;
656    }
657
658    ///Runs the algorithm from the given source node.
659
660    ///This method runs the %BFS algorithm from node \c s
661    ///in order to compute the shortest path to each node.
662    ///
663    ///The algorithm computes
664    ///- the shortest path tree,
665    ///- the distance of each node from the root.
666    ///
667    ///\note <tt>b.run(s)</tt> is just a shortcut of the following code.
668    ///\code
669    ///  b.init();
670    ///  b.addSource(s);
671    ///  b.start();
672    ///\endcode
673    void run(Node s) {
674      init();
675      addSource(s);
676      start();
677    }
678
679    ///Finds the shortest path between \c s and \c t.
680
681    ///This method runs the %BFS algorithm from node \c s
682    ///in order to compute the shortest path to node \c t
683    ///(it stops searching when \c t is processed).
684    ///
685    ///\return \c true if \c t is reachable form \c s.
686    ///
687    ///\note Apart from the return value, <tt>b.run(s,t)</tt> is just a
688    ///shortcut of the following code.
689    ///\code
690    ///  b.init();
691    ///  b.addSource(s);
692    ///  b.start(t);
693    ///\endcode
694    bool run(Node s,Node t) {
695      init();
696      addSource(s);
697      start(t);
698      return reached(t);
699    }
700
701    ///Runs the algorithm to visit all nodes in the digraph.
702
703    ///This method runs the %BFS algorithm in order to
704    ///compute the shortest path to each node.
705    ///
706    ///The algorithm computes
707    ///- the shortest path tree (forest),
708    ///- the distance of each node from the root(s).
709    ///
710    ///\note <tt>b.run(s)</tt> is just a shortcut of the following code.
711    ///\code
712    ///  b.init();
713    ///  for (NodeIt n(gr); n != INVALID; ++n) {
714    ///    if (!b.reached(n)) {
715    ///      b.addSource(n);
716    ///      b.start();
717    ///    }
718    ///  }
719    ///\endcode
720    void run() {
721      init();
722      for (NodeIt n(*G); n != INVALID; ++n) {
723        if (!reached(n)) {
724          addSource(n);
725          start();
726        }
727      }
728    }
729
730    ///@}
731
732    ///\name Query Functions
733    ///The results of the BFS algorithm can be obtained using these
734    ///functions.\n
735    ///Either \ref run(Node) "run()" or \ref start() should be called
736    ///before using them.
737
738    ///@{
739
740    ///The shortest path to a node.
741
742    ///Returns the shortest path to a node.
743    ///
744    ///\warning \c t should be reached from the root(s).
745    ///
746    ///\pre Either \ref run(Node) "run()" or \ref init()
747    ///must be called before using this function.
748    Path path(Node t) const { return Path(*G, *_pred, t); }
749
750    ///The distance of a node from the root(s).
751
752    ///Returns the distance of a node from the root(s).
753    ///
754    ///\warning If node \c v is not reached from the root(s), then
755    ///the return value of this function is undefined.
756    ///
757    ///\pre Either \ref run(Node) "run()" or \ref init()
758    ///must be called before using this function.
759    int dist(Node v) const { return (*_dist)[v]; }
760
761    ///Returns the 'previous arc' of the shortest path tree for a node.
762
763    ///This function returns the 'previous arc' of the shortest path
764    ///tree for the node \c v, i.e. it returns the last arc of a
765    ///shortest path from a root to \c v. It is \c INVALID if \c v
766    ///is not reached from the root(s) or if \c v is a root.
767    ///
768    ///The shortest path tree used here is equal to the shortest path
769    ///tree used in \ref predNode().
770    ///
771    ///\pre Either \ref run(Node) "run()" or \ref init()
772    ///must be called before using this function.
773    Arc predArc(Node v) const { return (*_pred)[v];}
774
775    ///Returns the 'previous node' of the shortest path tree for a node.
776
777    ///This function returns the 'previous node' of the shortest path
778    ///tree for the node \c v, i.e. it returns the last but one node
779    ///from a shortest path from a root to \c v. It is \c INVALID
780    ///if \c v is not reached from the root(s) or if \c v is a root.
781    ///
782    ///The shortest path tree used here is equal to the shortest path
783    ///tree used in \ref predArc().
784    ///
785    ///\pre Either \ref run(Node) "run()" or \ref init()
786    ///must be called before using this function.
787    Node predNode(Node v) const { return (*_pred)[v]==INVALID ? INVALID:
788                                  G->source((*_pred)[v]); }
789
790    ///\brief Returns a const reference to the node map that stores the
791    /// distances of the nodes.
792    ///
793    ///Returns a const reference to the node map that stores the distances
794    ///of the nodes calculated by the algorithm.
795    ///
796    ///\pre Either \ref run(Node) "run()" or \ref init()
797    ///must be called before using this function.
798    const DistMap &distMap() const { return *_dist;}
799
800    ///\brief Returns a const reference to the node map that stores the
801    ///predecessor arcs.
802    ///
803    ///Returns a const reference to the node map that stores the predecessor
804    ///arcs, which form the shortest path tree.
805    ///
806    ///\pre Either \ref run(Node) "run()" or \ref init()
807    ///must be called before using this function.
808    const PredMap &predMap() const { return *_pred;}
809
810    ///Checks if a node is reached from the root(s).
811
812    ///Returns \c true if \c v is reached from the root(s).
813    ///
814    ///\pre Either \ref run(Node) "run()" or \ref init()
815    ///must be called before using this function.
816    bool reached(Node v) const { return (*_reached)[v]; }
817
818    ///@}
819  };
820
821  ///Default traits class of bfs() function.
822
823  ///Default traits class of bfs() function.
824  ///\tparam GR Digraph type.
825  template<class GR>
826  struct BfsWizardDefaultTraits
827  {
828    ///The type of the digraph the algorithm runs on.
829    typedef GR Digraph;
830
831    ///\brief The type of the map that stores the predecessor
832    ///arcs of the shortest paths.
833    ///
834    ///The type of the map that stores the predecessor
835    ///arcs of the shortest paths.
836    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
837    typedef typename Digraph::template NodeMap<typename Digraph::Arc> PredMap;
838    ///Instantiates a PredMap.
839
840    ///This function instantiates a PredMap.
841    ///\param g is the digraph, to which we would like to define the
842    ///PredMap.
843    static PredMap *createPredMap(const Digraph &g)
844    {
845      return new PredMap(g);
846    }
847
848    ///The type of the map that indicates which nodes are processed.
849
850    ///The type of the map that indicates which nodes are processed.
851    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
852    ///By default it is a NullMap.
853    typedef NullMap<typename Digraph::Node,bool> ProcessedMap;
854    ///Instantiates a ProcessedMap.
855
856    ///This function instantiates a ProcessedMap.
857    ///\param g is the digraph, to which
858    ///we would like to define the ProcessedMap.
859#ifdef DOXYGEN
860    static ProcessedMap *createProcessedMap(const Digraph &g)
861#else
862    static ProcessedMap *createProcessedMap(const Digraph &)
863#endif
864    {
865      return new ProcessedMap();
866    }
867
868    ///The type of the map that indicates which nodes are reached.
869
870    ///The type of the map that indicates which nodes are reached.
871    ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
872    typedef typename Digraph::template NodeMap<bool> ReachedMap;
873    ///Instantiates a ReachedMap.
874
875    ///This function instantiates a ReachedMap.
876    ///\param g is the digraph, to which
877    ///we would like to define the ReachedMap.
878    static ReachedMap *createReachedMap(const Digraph &g)
879    {
880      return new ReachedMap(g);
881    }
882
883    ///The type of the map that stores the distances of the nodes.
884
885    ///The type of the map that stores the distances of the nodes.
886    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
887    typedef typename Digraph::template NodeMap<int> DistMap;
888    ///Instantiates a DistMap.
889
890    ///This function instantiates a DistMap.
891    ///\param g is the digraph, to which we would like to define
892    ///the DistMap
893    static DistMap *createDistMap(const Digraph &g)
894    {
895      return new DistMap(g);
896    }
897
898    ///The type of the shortest paths.
899
900    ///The type of the shortest paths.
901    ///It must meet the \ref concepts::Path "Path" concept.
902    typedef lemon::Path<Digraph> Path;
903  };
904
905  /// Default traits class used by BfsWizard
906
907  /// To make it easier to use Bfs algorithm
908  /// we have created a wizard class.
909  /// This \ref BfsWizard class needs default traits,
910  /// as well as the \ref Bfs class.
911  /// The \ref BfsWizardBase is a class to be the default traits of the
912  /// \ref BfsWizard class.
913  template<class GR>
914  class BfsWizardBase : public BfsWizardDefaultTraits<GR>
915  {
916
917    typedef BfsWizardDefaultTraits<GR> Base;
918  protected:
919    //The type of the nodes in the digraph.
920    typedef typename Base::Digraph::Node Node;
921
922    //Pointer to the digraph the algorithm runs on.
923    void *_g;
924    //Pointer to the map of reached nodes.
925    void *_reached;
926    //Pointer to the map of processed nodes.
927    void *_processed;
928    //Pointer to the map of predecessors arcs.
929    void *_pred;
930    //Pointer to the map of distances.
931    void *_dist;
932    //Pointer to the shortest path to the target node.
933    void *_path;
934    //Pointer to the distance of the target node.
935    int *_di;
936
937    public:
938    /// Constructor.
939
940    /// This constructor does not require parameters, therefore it initiates
941    /// all of the attributes to \c 0.
942    BfsWizardBase() : _g(0), _reached(0), _processed(0), _pred(0),
943                      _dist(0), _path(0), _di(0) {}
944
945    /// Constructor.
946
947    /// This constructor requires one parameter,
948    /// others are initiated to \c 0.
949    /// \param g The digraph the algorithm runs on.
950    BfsWizardBase(const GR &g) :
951      _g(reinterpret_cast<void*>(const_cast<GR*>(&g))),
952      _reached(0), _processed(0), _pred(0), _dist(0),  _path(0), _di(0) {}
953
954  };
955
956  /// Auxiliary class for the function-type interface of BFS algorithm.
957
958  /// This auxiliary class is created to implement the
959  /// \ref bfs() "function-type interface" of \ref Bfs algorithm.
960  /// It does not have own \ref run(Node) "run()" method, it uses the
961  /// functions and features of the plain \ref Bfs.
962  ///
963  /// This class should only be used through the \ref bfs() function,
964  /// which makes it easier to use the algorithm.
965  template<class TR>
966  class BfsWizard : public TR
967  {
968    typedef TR Base;
969
970    ///The type of the digraph the algorithm runs on.
971    typedef typename TR::Digraph Digraph;
972
973    typedef typename Digraph::Node Node;
974    typedef typename Digraph::NodeIt NodeIt;
975    typedef typename Digraph::Arc Arc;
976    typedef typename Digraph::OutArcIt OutArcIt;
977
978    ///\brief The type of the map that stores the predecessor
979    ///arcs of the shortest paths.
980    typedef typename TR::PredMap PredMap;
981    ///\brief The type of the map that stores the distances of the nodes.
982    typedef typename TR::DistMap DistMap;
983    ///\brief The type of the map that indicates which nodes are reached.
984    typedef typename TR::ReachedMap ReachedMap;
985    ///\brief The type of the map that indicates which nodes are processed.
986    typedef typename TR::ProcessedMap ProcessedMap;
987    ///The type of the shortest paths
988    typedef typename TR::Path Path;
989
990  public:
991
992    /// Constructor.
993    BfsWizard() : TR() {}
994
995    /// Constructor that requires parameters.
996
997    /// Constructor that requires parameters.
998    /// These parameters will be the default values for the traits class.
999    /// \param g The digraph the algorithm runs on.
1000    BfsWizard(const Digraph &g) :
1001      TR(g) {}
1002
1003    ///Copy constructor
1004    BfsWizard(const TR &b) : TR(b) {}
1005
1006    ~BfsWizard() {}
1007
1008    ///Runs BFS algorithm from the given source node.
1009
1010    ///This method runs BFS algorithm from node \c s
1011    ///in order to compute the shortest path to each node.
1012    void run(Node s)
1013    {
1014      Bfs<Digraph,TR> alg(*reinterpret_cast<const Digraph*>(Base::_g));
1015      if (Base::_pred)
1016        alg.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
1017      if (Base::_dist)
1018        alg.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
1019      if (Base::_reached)
1020        alg.reachedMap(*reinterpret_cast<ReachedMap*>(Base::_reached));
1021      if (Base::_processed)
1022        alg.processedMap(*reinterpret_cast<ProcessedMap*>(Base::_processed));
1023      if (s!=INVALID)
1024        alg.run(s);
1025      else
1026        alg.run();
1027    }
1028
1029    ///Finds the shortest path between \c s and \c t.
1030
1031    ///This method runs BFS algorithm from node \c s
1032    ///in order to compute the shortest path to node \c t
1033    ///(it stops searching when \c t is processed).
1034    ///
1035    ///\return \c true if \c t is reachable form \c s.
1036    bool run(Node s, Node t)
1037    {
1038      Bfs<Digraph,TR> alg(*reinterpret_cast<const Digraph*>(Base::_g));
1039      if (Base::_pred)
1040        alg.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
1041      if (Base::_dist)
1042        alg.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
1043      if (Base::_reached)
1044        alg.reachedMap(*reinterpret_cast<ReachedMap*>(Base::_reached));
1045      if (Base::_processed)
1046        alg.processedMap(*reinterpret_cast<ProcessedMap*>(Base::_processed));
1047      alg.run(s,t);
1048      if (Base::_path)
1049        *reinterpret_cast<Path*>(Base::_path) = alg.path(t);
1050      if (Base::_di)
1051        *Base::_di = alg.dist(t);
1052      return alg.reached(t);
1053    }
1054
1055    ///Runs BFS algorithm to visit all nodes in the digraph.
1056
1057    ///This method runs BFS algorithm in order to compute
1058    ///the shortest path to each node.
1059    void run()
1060    {
1061      run(INVALID);
1062    }
1063
1064    template<class T>
1065    struct SetPredMapBase : public Base {
1066      typedef T PredMap;
1067      static PredMap *createPredMap(const Digraph &) { return 0; };
1068      SetPredMapBase(const TR &b) : TR(b) {}
1069    };
1070    ///\brief \ref named-func-param "Named parameter"
1071    ///for setting PredMap object.
1072    ///
1073    ///\ref named-func-param "Named parameter"
1074    ///for setting PredMap object.
1075    template<class T>
1076    BfsWizard<SetPredMapBase<T> > predMap(const T &t)
1077    {
1078      Base::_pred=reinterpret_cast<void*>(const_cast<T*>(&t));
1079      return BfsWizard<SetPredMapBase<T> >(*this);
1080    }
1081
1082    template<class T>
1083    struct SetReachedMapBase : public Base {
1084      typedef T ReachedMap;
1085      static ReachedMap *createReachedMap(const Digraph &) { return 0; };
1086      SetReachedMapBase(const TR &b) : TR(b) {}
1087    };
1088    ///\brief \ref named-func-param "Named parameter"
1089    ///for setting ReachedMap object.
1090    ///
1091    /// \ref named-func-param "Named parameter"
1092    ///for setting ReachedMap object.
1093    template<class T>
1094    BfsWizard<SetReachedMapBase<T> > reachedMap(const T &t)
1095    {
1096      Base::_reached=reinterpret_cast<void*>(const_cast<T*>(&t));
1097      return BfsWizard<SetReachedMapBase<T> >(*this);
1098    }
1099
1100    template<class T>
1101    struct SetDistMapBase : public Base {
1102      typedef T DistMap;
1103      static DistMap *createDistMap(const Digraph &) { return 0; };
1104      SetDistMapBase(const TR &b) : TR(b) {}
1105    };
1106    ///\brief \ref named-func-param "Named parameter"
1107    ///for setting DistMap object.
1108    ///
1109    /// \ref named-func-param "Named parameter"
1110    ///for setting DistMap object.
1111    template<class T>
1112    BfsWizard<SetDistMapBase<T> > distMap(const T &t)
1113    {
1114      Base::_dist=reinterpret_cast<void*>(const_cast<T*>(&t));
1115      return BfsWizard<SetDistMapBase<T> >(*this);
1116    }
1117
1118    template<class T>
1119    struct SetProcessedMapBase : public Base {
1120      typedef T ProcessedMap;
1121      static ProcessedMap *createProcessedMap(const Digraph &) { return 0; };
1122      SetProcessedMapBase(const TR &b) : TR(b) {}
1123    };
1124    ///\brief \ref named-func-param "Named parameter"
1125    ///for setting ProcessedMap object.
1126    ///
1127    /// \ref named-func-param "Named parameter"
1128    ///for setting ProcessedMap object.
1129    template<class T>
1130    BfsWizard<SetProcessedMapBase<T> > processedMap(const T &t)
1131    {
1132      Base::_processed=reinterpret_cast<void*>(const_cast<T*>(&t));
1133      return BfsWizard<SetProcessedMapBase<T> >(*this);
1134    }
1135
1136    template<class T>
1137    struct SetPathBase : public Base {
1138      typedef T Path;
1139      SetPathBase(const TR &b) : TR(b) {}
1140    };
1141    ///\brief \ref named-func-param "Named parameter"
1142    ///for getting the shortest path to the target node.
1143    ///
1144    ///\ref named-func-param "Named parameter"
1145    ///for getting the shortest path to the target node.
1146    template<class T>
1147    BfsWizard<SetPathBase<T> > path(const T &t)
1148    {
1149      Base::_path=reinterpret_cast<void*>(const_cast<T*>(&t));
1150      return BfsWizard<SetPathBase<T> >(*this);
1151    }
1152
1153    ///\brief \ref named-func-param "Named parameter"
1154    ///for getting the distance of the target node.
1155    ///
1156    ///\ref named-func-param "Named parameter"
1157    ///for getting the distance of the target node.
1158    BfsWizard dist(const int &d)
1159    {
1160      Base::_di=const_cast<int*>(&d);
1161      return *this;
1162    }
1163
1164  };
1165
1166  ///Function-type interface for BFS algorithm.
1167
1168  /// \ingroup search
1169  ///Function-type interface for BFS algorithm.
1170  ///
1171  ///This function also has several \ref named-func-param "named parameters",
1172  ///they are declared as the members of class \ref BfsWizard.
1173  ///The following examples show how to use these parameters.
1174  ///\code
1175  ///  // Compute shortest path from node s to each node
1176  ///  bfs(g).predMap(preds).distMap(dists).run(s);
1177  ///
1178  ///  // Compute shortest path from s to t
1179  ///  bool reached = bfs(g).path(p).dist(d).run(s,t);
1180  ///\endcode
1181  ///\warning Don't forget to put the \ref BfsWizard::run(Node) "run()"
1182  ///to the end of the parameter list.
1183  ///\sa BfsWizard
1184  ///\sa Bfs
1185  template<class GR>
1186  BfsWizard<BfsWizardBase<GR> >
1187  bfs(const GR &digraph)
1188  {
1189    return BfsWizard<BfsWizardBase<GR> >(digraph);
1190  }
1191
1192#ifdef DOXYGEN
1193  /// \brief Visitor class for BFS.
1194  ///
1195  /// This class defines the interface of the BfsVisit events, and
1196  /// it could be the base of a real visitor class.
1197  template <typename _Digraph>
1198  struct BfsVisitor {
1199    typedef _Digraph Digraph;
1200    typedef typename Digraph::Arc Arc;
1201    typedef typename Digraph::Node Node;
1202    /// \brief Called for the source node(s) of the BFS.
1203    ///
1204    /// This function is called for the source node(s) of the BFS.
1205    void start(const Node& node) {}
1206    /// \brief Called when a node is reached first time.
1207    ///
1208    /// This function is called when a node is reached first time.
1209    void reach(const Node& node) {}
1210    /// \brief Called when a node is processed.
1211    ///
1212    /// This function is called when a node is processed.
1213    void process(const Node& node) {}
1214    /// \brief Called when an arc reaches a new node.
1215    ///
1216    /// This function is called when the BFS finds an arc whose target node
1217    /// is not reached yet.
1218    void discover(const Arc& arc) {}
1219    /// \brief Called when an arc is examined but its target node is
1220    /// already discovered.
1221    ///
1222    /// This function is called when an arc is examined but its target node is
1223    /// already discovered.
1224    void examine(const Arc& arc) {}
1225  };
1226#else
1227  template <typename _Digraph>
1228  struct BfsVisitor {
1229    typedef _Digraph Digraph;
1230    typedef typename Digraph::Arc Arc;
1231    typedef typename Digraph::Node Node;
1232    void start(const Node&) {}
1233    void reach(const Node&) {}
1234    void process(const Node&) {}
1235    void discover(const Arc&) {}
1236    void examine(const Arc&) {}
1237
1238    template <typename _Visitor>
1239    struct Constraints {
1240      void constraints() {
1241        Arc arc;
1242        Node node;
1243        visitor.start(node);
1244        visitor.reach(node);
1245        visitor.process(node);
1246        visitor.discover(arc);
1247        visitor.examine(arc);
1248      }
1249      _Visitor& visitor;
1250    };
1251  };
1252#endif
1253
1254  /// \brief Default traits class of BfsVisit class.
1255  ///
1256  /// Default traits class of BfsVisit class.
1257  /// \tparam _Digraph The type of the digraph the algorithm runs on.
1258  template<class _Digraph>
1259  struct BfsVisitDefaultTraits {
1260
1261    /// \brief The type of the digraph the algorithm runs on.
1262    typedef _Digraph Digraph;
1263
1264    /// \brief The type of the map that indicates which nodes are reached.
1265    ///
1266    /// The type of the map that indicates which nodes are reached.
1267    /// It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
1268    typedef typename Digraph::template NodeMap<bool> ReachedMap;
1269
1270    /// \brief Instantiates a ReachedMap.
1271    ///
1272    /// This function instantiates a ReachedMap.
1273    /// \param digraph is the digraph, to which
1274    /// we would like to define the ReachedMap.
1275    static ReachedMap *createReachedMap(const Digraph &digraph) {
1276      return new ReachedMap(digraph);
1277    }
1278
1279  };
1280
1281  /// \ingroup search
1282  ///
1283  /// \brief %BFS algorithm class with visitor interface.
1284  ///
1285  /// This class provides an efficient implementation of the %BFS algorithm
1286  /// with visitor interface.
1287  ///
1288  /// The %BfsVisit class provides an alternative interface to the Bfs
1289  /// class. It works with callback mechanism, the BfsVisit object calls
1290  /// the member functions of the \c Visitor class on every BFS event.
1291  ///
1292  /// This interface of the BFS algorithm should be used in special cases
1293  /// when extra actions have to be performed in connection with certain
1294  /// events of the BFS algorithm. Otherwise consider to use Bfs or bfs()
1295  /// instead.
1296  ///
1297  /// \tparam _Digraph The type of the digraph the algorithm runs on.
1298  /// The default value is
1299  /// \ref ListDigraph. The value of _Digraph is not used directly by
1300  /// \ref BfsVisit, it is only passed to \ref BfsVisitDefaultTraits.
1301  /// \tparam _Visitor The Visitor type that is used by the algorithm.
1302  /// \ref BfsVisitor "BfsVisitor<_Digraph>" is an empty visitor, which
1303  /// does not observe the BFS events. If you want to observe the BFS
1304  /// events, you should implement your own visitor class.
1305  /// \tparam _Traits Traits class to set various data types used by the
1306  /// algorithm. The default traits class is
1307  /// \ref BfsVisitDefaultTraits "BfsVisitDefaultTraits<_Digraph>".
1308  /// See \ref BfsVisitDefaultTraits for the documentation of
1309  /// a BFS visit traits class.
1310#ifdef DOXYGEN
1311  template <typename _Digraph, typename _Visitor, typename _Traits>
1312#else
1313  template <typename _Digraph = ListDigraph,
1314            typename _Visitor = BfsVisitor<_Digraph>,
1315            typename _Traits = BfsVisitDefaultTraits<_Digraph> >
1316#endif
1317  class BfsVisit {
1318  public:
1319
1320    ///The traits class.
1321    typedef _Traits Traits;
1322
1323    ///The type of the digraph the algorithm runs on.
1324    typedef typename Traits::Digraph Digraph;
1325
1326    ///The visitor type used by the algorithm.
1327    typedef _Visitor Visitor;
1328
1329    ///The type of the map that indicates which nodes are reached.
1330    typedef typename Traits::ReachedMap ReachedMap;
1331
1332  private:
1333
1334    typedef typename Digraph::Node Node;
1335    typedef typename Digraph::NodeIt NodeIt;
1336    typedef typename Digraph::Arc Arc;
1337    typedef typename Digraph::OutArcIt OutArcIt;
1338
1339    //Pointer to the underlying digraph.
1340    const Digraph *_digraph;
1341    //Pointer to the visitor object.
1342    Visitor *_visitor;
1343    //Pointer to the map of reached status of the nodes.
1344    ReachedMap *_reached;
1345    //Indicates if _reached is locally allocated (true) or not.
1346    bool local_reached;
1347
1348    std::vector<typename Digraph::Node> _list;
1349    int _list_front, _list_back;
1350
1351    //Creates the maps if necessary.
1352    void create_maps() {
1353      if(!_reached) {
1354        local_reached = true;
1355        _reached = Traits::createReachedMap(*_digraph);
1356      }
1357    }
1358
1359  protected:
1360
1361    BfsVisit() {}
1362
1363  public:
1364
1365    typedef BfsVisit Create;
1366
1367    /// \name Named Template Parameters
1368
1369    ///@{
1370    template <class T>
1371    struct SetReachedMapTraits : public Traits {
1372      typedef T ReachedMap;
1373      static ReachedMap *createReachedMap(const Digraph &digraph) {
1374        LEMON_ASSERT(false, "ReachedMap is not initialized");
1375        return 0; // ignore warnings
1376      }
1377    };
1378    /// \brief \ref named-templ-param "Named parameter" for setting
1379    /// ReachedMap type.
1380    ///
1381    /// \ref named-templ-param "Named parameter" for setting ReachedMap type.
1382    template <class T>
1383    struct SetReachedMap : public BfsVisit< Digraph, Visitor,
1384                                            SetReachedMapTraits<T> > {
1385      typedef BfsVisit< Digraph, Visitor, SetReachedMapTraits<T> > Create;
1386    };
1387    ///@}
1388
1389  public:
1390
1391    /// \brief Constructor.
1392    ///
1393    /// Constructor.
1394    ///
1395    /// \param digraph The digraph the algorithm runs on.
1396    /// \param visitor The visitor object of the algorithm.
1397    BfsVisit(const Digraph& digraph, Visitor& visitor)
1398      : _digraph(&digraph), _visitor(&visitor),
1399        _reached(0), local_reached(false) {}
1400
1401    /// \brief Destructor.
1402    ~BfsVisit() {
1403      if(local_reached) delete _reached;
1404    }
1405
1406    /// \brief Sets the map that indicates which nodes are reached.
1407    ///
1408    /// Sets the map that indicates which nodes are reached.
1409    /// If you don't use this function before calling \ref run(Node) "run()"
1410    /// or \ref init(), an instance will be allocated automatically.
1411    /// The destructor deallocates this automatically allocated map,
1412    /// of course.
1413    /// \return <tt> (*this) </tt>
1414    BfsVisit &reachedMap(ReachedMap &m) {
1415      if(local_reached) {
1416        delete _reached;
1417        local_reached = false;
1418      }
1419      _reached = &m;
1420      return *this;
1421    }
1422
1423  public:
1424
1425    /// \name Execution Control
1426    /// The simplest way to execute the BFS algorithm is to use one of the
1427    /// member functions called \ref run(Node) "run()".\n
1428    /// If you need more control on the execution, first you have to call
1429    /// \ref init(), then you can add several source nodes with
1430    /// \ref addSource(). Finally the actual path computation can be
1431    /// performed with one of the \ref start() functions.
1432
1433    /// @{
1434
1435    /// \brief Initializes the internal data structures.
1436    ///
1437    /// Initializes the internal data structures.
1438    void init() {
1439      create_maps();
1440      _list.resize(countNodes(*_digraph));
1441      _list_front = _list_back = -1;
1442      for (NodeIt u(*_digraph) ; u != INVALID ; ++u) {
1443        _reached->set(u, false);
1444      }
1445    }
1446
1447    /// \brief Adds a new source node.
1448    ///
1449    /// Adds a new source node to the set of nodes to be processed.
1450    void addSource(Node s) {
1451      if(!(*_reached)[s]) {
1452          _reached->set(s,true);
1453          _visitor->start(s);
1454          _visitor->reach(s);
1455          _list[++_list_back] = s;
1456        }
1457    }
1458
1459    /// \brief Processes the next node.
1460    ///
1461    /// Processes the next node.
1462    ///
1463    /// \return The processed node.
1464    ///
1465    /// \pre The queue must not be empty.
1466    Node processNextNode() {
1467      Node n = _list[++_list_front];
1468      _visitor->process(n);
1469      Arc e;
1470      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
1471        Node m = _digraph->target(e);
1472        if (!(*_reached)[m]) {
1473          _visitor->discover(e);
1474          _visitor->reach(m);
1475          _reached->set(m, true);
1476          _list[++_list_back] = m;
1477        } else {
1478          _visitor->examine(e);
1479        }
1480      }
1481      return n;
1482    }
1483
1484    /// \brief Processes the next node.
1485    ///
1486    /// Processes the next node and checks if the given target node
1487    /// is reached. If the target node is reachable from the processed
1488    /// node, then the \c reach parameter will be set to \c true.
1489    ///
1490    /// \param target The target node.
1491    /// \retval reach Indicates if the target node is reached.
1492    /// It should be initially \c false.
1493    ///
1494    /// \return The processed node.
1495    ///
1496    /// \pre The queue must not be empty.
1497    Node processNextNode(Node target, bool& reach) {
1498      Node n = _list[++_list_front];
1499      _visitor->process(n);
1500      Arc e;
1501      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
1502        Node m = _digraph->target(e);
1503        if (!(*_reached)[m]) {
1504          _visitor->discover(e);
1505          _visitor->reach(m);
1506          _reached->set(m, true);
1507          _list[++_list_back] = m;
1508          reach = reach || (target == m);
1509        } else {
1510          _visitor->examine(e);
1511        }
1512      }
1513      return n;
1514    }
1515
1516    /// \brief Processes the next node.
1517    ///
1518    /// Processes the next node and checks if at least one of reached
1519    /// nodes has \c true value in the \c nm node map. If one node
1520    /// with \c true value is reachable from the processed node, then the
1521    /// \c rnode parameter will be set to the first of such nodes.
1522    ///
1523    /// \param nm A \c bool (or convertible) node map that indicates the
1524    /// possible targets.
1525    /// \retval rnode The reached target node.
1526    /// It should be initially \c INVALID.
1527    ///
1528    /// \return The processed node.
1529    ///
1530    /// \pre The queue must not be empty.
1531    template <typename NM>
1532    Node processNextNode(const NM& nm, Node& rnode) {
1533      Node n = _list[++_list_front];
1534      _visitor->process(n);
1535      Arc e;
1536      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
1537        Node m = _digraph->target(e);
1538        if (!(*_reached)[m]) {
1539          _visitor->discover(e);
1540          _visitor->reach(m);
1541          _reached->set(m, true);
1542          _list[++_list_back] = m;
1543          if (nm[m] && rnode == INVALID) rnode = m;
1544        } else {
1545          _visitor->examine(e);
1546        }
1547      }
1548      return n;
1549    }
1550
1551    /// \brief The next node to be processed.
1552    ///
1553    /// Returns the next node to be processed or \c INVALID if the queue
1554    /// is empty.
1555    Node nextNode() const {
1556      return _list_front != _list_back ? _list[_list_front + 1] : INVALID;
1557    }
1558
1559    /// \brief Returns \c false if there are nodes
1560    /// to be processed.
1561    ///
1562    /// Returns \c false if there are nodes
1563    /// to be processed in the queue.
1564    bool emptyQueue() const { return _list_front == _list_back; }
1565
1566    /// \brief Returns the number of the nodes to be processed.
1567    ///
1568    /// Returns the number of the nodes to be processed in the queue.
1569    int queueSize() const { return _list_back - _list_front; }
1570
1571    /// \brief Executes the algorithm.
1572    ///
1573    /// Executes the algorithm.
1574    ///
1575    /// This method runs the %BFS algorithm from the root node(s)
1576    /// in order to compute the shortest path to each node.
1577    ///
1578    /// The algorithm computes
1579    /// - the shortest path tree (forest),
1580    /// - the distance of each node from the root(s).
1581    ///
1582    /// \pre init() must be called and at least one root node should be added
1583    /// with addSource() before using this function.
1584    ///
1585    /// \note <tt>b.start()</tt> is just a shortcut of the following code.
1586    /// \code
1587    ///   while ( !b.emptyQueue() ) {
1588    ///     b.processNextNode();
1589    ///   }
1590    /// \endcode
1591    void start() {
1592      while ( !emptyQueue() ) processNextNode();
1593    }
1594
1595    /// \brief Executes the algorithm until the given target node is reached.
1596    ///
1597    /// Executes the algorithm until the given target node is reached.
1598    ///
1599    /// This method runs the %BFS algorithm from the root node(s)
1600    /// in order to compute the shortest path to \c t.
1601    ///
1602    /// The algorithm computes
1603    /// - the shortest path to \c t,
1604    /// - the distance of \c t from the root(s).
1605    ///
1606    /// \pre init() must be called and at least one root node should be
1607    /// added with addSource() before using this function.
1608    ///
1609    /// \note <tt>b.start(t)</tt> is just a shortcut of the following code.
1610    /// \code
1611    ///   bool reach = false;
1612    ///   while ( !b.emptyQueue() && !reach ) {
1613    ///     b.processNextNode(t, reach);
1614    ///   }
1615    /// \endcode
1616    void start(Node t) {
1617      bool reach = false;
1618      while ( !emptyQueue() && !reach ) processNextNode(t, reach);
1619    }
1620
1621    /// \brief Executes the algorithm until a condition is met.
1622    ///
1623    /// Executes the algorithm until a condition is met.
1624    ///
1625    /// This method runs the %BFS algorithm from the root node(s) in
1626    /// order to compute the shortest path to a node \c v with
1627    /// <tt>nm[v]</tt> true, if such a node can be found.
1628    ///
1629    /// \param nm must be a bool (or convertible) node map. The
1630    /// algorithm will stop when it reaches a node \c v with
1631    /// <tt>nm[v]</tt> true.
1632    ///
1633    /// \return The reached node \c v with <tt>nm[v]</tt> true or
1634    /// \c INVALID if no such node was found.
1635    ///
1636    /// \pre init() must be called and at least one root node should be
1637    /// added with addSource() before using this function.
1638    ///
1639    /// \note <tt>b.start(nm)</tt> is just a shortcut of the following code.
1640    /// \code
1641    ///   Node rnode = INVALID;
1642    ///   while ( !b.emptyQueue() && rnode == INVALID ) {
1643    ///     b.processNextNode(nm, rnode);
1644    ///   }
1645    ///   return rnode;
1646    /// \endcode
1647    template <typename NM>
1648    Node start(const NM &nm) {
1649      Node rnode = INVALID;
1650      while ( !emptyQueue() && rnode == INVALID ) {
1651        processNextNode(nm, rnode);
1652      }
1653      return rnode;
1654    }
1655
1656    /// \brief Runs the algorithm from the given source node.
1657    ///
1658    /// This method runs the %BFS algorithm from node \c s
1659    /// in order to compute the shortest path to each node.
1660    ///
1661    /// The algorithm computes
1662    /// - the shortest path tree,
1663    /// - the distance of each node from the root.
1664    ///
1665    /// \note <tt>b.run(s)</tt> is just a shortcut of the following code.
1666    ///\code
1667    ///   b.init();
1668    ///   b.addSource(s);
1669    ///   b.start();
1670    ///\endcode
1671    void run(Node s) {
1672      init();
1673      addSource(s);
1674      start();
1675    }
1676
1677    /// \brief Finds the shortest path between \c s and \c t.
1678    ///
1679    /// This method runs the %BFS algorithm from node \c s
1680    /// in order to compute the shortest path to node \c t
1681    /// (it stops searching when \c t is processed).
1682    ///
1683    /// \return \c true if \c t is reachable form \c s.
1684    ///
1685    /// \note Apart from the return value, <tt>b.run(s,t)</tt> is just a
1686    /// shortcut of the following code.
1687    ///\code
1688    ///   b.init();
1689    ///   b.addSource(s);
1690    ///   b.start(t);
1691    ///\endcode
1692    bool run(Node s,Node t) {
1693      init();
1694      addSource(s);
1695      start(t);
1696      return reached(t);
1697    }
1698
1699    /// \brief Runs the algorithm to visit all nodes in the digraph.
1700    ///
1701    /// This method runs the %BFS algorithm in order to
1702    /// compute the shortest path to each node.
1703    ///
1704    /// The algorithm computes
1705    /// - the shortest path tree (forest),
1706    /// - the distance of each node from the root(s).
1707    ///
1708    /// \note <tt>b.run(s)</tt> is just a shortcut of the following code.
1709    ///\code
1710    ///  b.init();
1711    ///  for (NodeIt n(gr); n != INVALID; ++n) {
1712    ///    if (!b.reached(n)) {
1713    ///      b.addSource(n);
1714    ///      b.start();
1715    ///    }
1716    ///  }
1717    ///\endcode
1718    void run() {
1719      init();
1720      for (NodeIt it(*_digraph); it != INVALID; ++it) {
1721        if (!reached(it)) {
1722          addSource(it);
1723          start();
1724        }
1725      }
1726    }
1727
1728    ///@}
1729
1730    /// \name Query Functions
1731    /// The results of the BFS algorithm can be obtained using these
1732    /// functions.\n
1733    /// Either \ref run(Node) "run()" or \ref start() should be called
1734    /// before using them.
1735
1736    ///@{
1737
1738    /// \brief Checks if a node is reached from the root(s).
1739    ///
1740    /// Returns \c true if \c v is reached from the root(s).
1741    ///
1742    /// \pre Either \ref run(Node) "run()" or \ref init()
1743    /// must be called before using this function.
1744    bool reached(Node v) const { return (*_reached)[v]; }
1745
1746    ///@}
1747
1748  };
1749
1750} //END OF NAMESPACE LEMON
1751
1752#endif
Note: See TracBrowser for help on using the repository browser.