COIN-OR::LEMON - Graph Library

source: lemon-1.2/lemon/bfs.h @ 788:c92296660262

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