COIN-OR::LEMON - Graph Library

source: lemon/lemon/bfs.h @ 247:f1158744a112

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1/* -*- mode: C++; indent-tabs-mode: nil; -*-
2 *
3 * This file is a part of LEMON, a generic C++ optimization library.
4 *
5 * Copyright (C) 2003-2008
6 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
7 * (Egervary Research Group on Combinatorial Optimization, EGRES).
8 *
9 * Permission to use, modify and distribute this software is granted
10 * provided that this copyright notice appears in all copies. For
11 * precise terms see the accompanying LICENSE file.
12 *
13 * This software is provided "AS IS" with no warranty of any kind,
14 * express or implied, and with no claim as to its suitability for any
15 * purpose.
16 *
17 */
18
19#ifndef LEMON_BFS_H
20#define LEMON_BFS_H
21
22///\ingroup search
23///\file
24///\brief BFS algorithm.
25
26#include <lemon/list_graph.h>
27#include <lemon/bits/path_dump.h>
28#include <lemon/core.h>
29#include <lemon/error.h>
30#include <lemon/maps.h>
31
32namespace lemon {
33
34  ///Default traits class of Bfs class.
35
36  ///Default traits class of Bfs class.
37  ///\tparam GR Digraph type.
38  template<class GR>
39  struct BfsDefaultTraits
40  {
41    ///The type of the digraph the algorithm runs on.
42    typedef GR Digraph;
43
44    ///\brief The type of the map that stores the predecessor
45    ///arcs of the shortest paths.
46    ///
47    ///The type of the map that stores the predecessor
48    ///arcs of the shortest paths.
49    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
50    typedef typename Digraph::template NodeMap<typename Digraph::Arc> PredMap;
51    ///Instantiates a \ref PredMap.
52
53    ///This function instantiates a \ref PredMap.
54    ///\param g is the digraph, to which we would like to define the
55    ///\ref PredMap.
56    ///\todo The digraph alone may be insufficient to initialize
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    ///By default it is a NullMap.
67    typedef NullMap<typename Digraph::Node,bool> ProcessedMap;
68    ///Instantiates a \ref 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 meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
86    typedef typename Digraph::template NodeMap<bool> ReachedMap;
87    ///Instantiates a \ref 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 meet the \ref concepts::WriteMap "WriteMap" concept.
101    typedef typename Digraph::template NodeMap<int> DistMap;
102    ///Instantiates a \ref 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 value is \ref ListDigraph. The value of GR is not used
124  ///directly by \ref Bfs, it is only passed to \ref BfsDefaultTraits.
125  ///\tparam TR Traits class to set various data types used by the algorithm.
126  ///The default traits class is
127  ///\ref BfsDefaultTraits "BfsDefaultTraits<GR>".
128  ///See \ref BfsDefaultTraits for the documentation of
129  ///a Bfs traits class.
130#ifdef DOXYGEN
131  template <typename GR,
132            typename TR>
133#else
134  template <typename GR=ListDigraph,
135            typename TR=BfsDefaultTraits<GR> >
136#endif
137  class Bfs {
138  public:
139    ///\ref Exception for uninitialized parameters.
140
141    ///This error represents problems in the initialization of the
142    ///parameters of the algorithm.
143    class UninitializedParameter : public lemon::UninitializedParameter {
144    public:
145      virtual const char* what() const throw() {
146        return "lemon::Bfs::UninitializedParameter";
147      }
148    };
149
150    ///The type of the digraph the algorithm runs on.
151    typedef typename TR::Digraph Digraph;
152
153    ///\brief The type of the map that stores the predecessor arcs of the
154    ///shortest paths.
155    typedef typename TR::PredMap PredMap;
156    ///The type of the map that stores the distances of the nodes.
157    typedef typename TR::DistMap DistMap;
158    ///The type of the map that indicates which nodes are reached.
159    typedef typename TR::ReachedMap ReachedMap;
160    ///The type of the map that indicates which nodes are processed.
161    typedef typename TR::ProcessedMap ProcessedMap;
162    ///The type of the paths.
163    typedef PredMapPath<Digraph, PredMap> Path;
164
165    ///The traits class.
166    typedef TR Traits;
167
168  private:
169
170    typedef typename Digraph::Node Node;
171    typedef typename Digraph::NodeIt NodeIt;
172    typedef typename Digraph::Arc Arc;
173    typedef typename Digraph::OutArcIt OutArcIt;
174
175    //Pointer to the underlying digraph.
176    const Digraph *G;
177    //Pointer to the map of predecessor arcs.
178    PredMap *_pred;
179    //Indicates if _pred is locally allocated (true) or not.
180    bool local_pred;
181    //Pointer to the map of distances.
182    DistMap *_dist;
183    //Indicates if _dist is locally allocated (true) or not.
184    bool local_dist;
185    //Pointer to the map of reached status of the nodes.
186    ReachedMap *_reached;
187    //Indicates if _reached is locally allocated (true) or not.
188    bool local_reached;
189    //Pointer to the map of processed status of the nodes.
190    ProcessedMap *_processed;
191    //Indicates if _processed is locally allocated (true) or not.
192    bool local_processed;
193
194    std::vector<typename Digraph::Node> _queue;
195    int _queue_head,_queue_tail,_queue_next_dist;
196    int _curr_dist;
197
198    ///Creates the maps if necessary.
199    ///\todo Better memory allocation (instead of new).
200    void create_maps()
201    {
202      if(!_pred) {
203        local_pred = true;
204        _pred = Traits::createPredMap(*G);
205      }
206      if(!_dist) {
207        local_dist = true;
208        _dist = Traits::createDistMap(*G);
209      }
210      if(!_reached) {
211        local_reached = true;
212        _reached = Traits::createReachedMap(*G);
213      }
214      if(!_processed) {
215        local_processed = true;
216        _processed = Traits::createProcessedMap(*G);
217      }
218    }
219
220  protected:
221
222    Bfs() {}
223
224  public:
225
226    typedef Bfs Create;
227
228    ///\name Named template parameters
229
230    ///@{
231
232    template <class T>
233    struct DefPredMapTraits : public Traits {
234      typedef T PredMap;
235      static PredMap *createPredMap(const Digraph &)
236      {
237        throw UninitializedParameter();
238      }
239    };
240    ///\brief \ref named-templ-param "Named parameter" for setting
241    ///\ref PredMap type.
242    ///
243    ///\ref named-templ-param "Named parameter" for setting
244    ///\ref PredMap type.
245    template <class T>
246    struct DefPredMap : public Bfs< Digraph, DefPredMapTraits<T> > {
247      typedef Bfs< Digraph, DefPredMapTraits<T> > Create;
248    };
249
250    template <class T>
251    struct DefDistMapTraits : public Traits {
252      typedef T DistMap;
253      static DistMap *createDistMap(const Digraph &)
254      {
255        throw UninitializedParameter();
256      }
257    };
258    ///\brief \ref named-templ-param "Named parameter" for setting
259    ///\ref DistMap type.
260    ///
261    ///\ref named-templ-param "Named parameter" for setting
262    ///\ref DistMap type.
263    template <class T>
264    struct DefDistMap : public Bfs< Digraph, DefDistMapTraits<T> > {
265      typedef Bfs< Digraph, DefDistMapTraits<T> > Create;
266    };
267
268    template <class T>
269    struct DefReachedMapTraits : public Traits {
270      typedef T ReachedMap;
271      static ReachedMap *createReachedMap(const Digraph &)
272      {
273        throw UninitializedParameter();
274      }
275    };
276    ///\brief \ref named-templ-param "Named parameter" for setting
277    ///\ref ReachedMap type.
278    ///
279    ///\ref named-templ-param "Named parameter" for setting
280    ///\ref ReachedMap type.
281    template <class T>
282    struct DefReachedMap : public Bfs< Digraph, DefReachedMapTraits<T> > {
283      typedef Bfs< Digraph, DefReachedMapTraits<T> > Create;
284    };
285
286    template <class T>
287    struct DefProcessedMapTraits : public Traits {
288      typedef T ProcessedMap;
289      static ProcessedMap *createProcessedMap(const Digraph &)
290      {
291        throw UninitializedParameter();
292      }
293    };
294    ///\brief \ref named-templ-param "Named parameter" for setting
295    ///\ref ProcessedMap type.
296    ///
297    ///\ref named-templ-param "Named parameter" for setting
298    ///\ref ProcessedMap type.
299    template <class T>
300    struct DefProcessedMap : public Bfs< Digraph, DefProcessedMapTraits<T> > {
301      typedef Bfs< Digraph, DefProcessedMapTraits<T> > Create;
302    };
303
304    struct DefDigraphProcessedMapTraits : public Traits {
305      typedef typename Digraph::template NodeMap<bool> ProcessedMap;
306      static ProcessedMap *createProcessedMap(const Digraph &g)
307      {
308        return new ProcessedMap(g);
309      }
310    };
311    ///\brief \ref named-templ-param "Named parameter" for setting
312    ///\ref ProcessedMap type to be <tt>Digraph::NodeMap<bool></tt>.
313    ///
314    ///\ref named-templ-param "Named parameter" for setting
315    ///\ref ProcessedMap type to be <tt>Digraph::NodeMap<bool></tt>.
316    ///If you don't set it explicitly, it will be automatically allocated.
317    template <class T>
318    struct DefProcessedMapToBeDefaultMap :
319      public Bfs< Digraph, DefDigraphProcessedMapTraits> {
320      typedef Bfs< Digraph, DefDigraphProcessedMapTraits> Create;
321    };
322
323    ///@}
324
325  public:
326
327    ///Constructor.
328
329    ///Constructor.
330    ///\param g The digraph the algorithm runs on.
331    Bfs(const Digraph &g) :
332      G(&g),
333      _pred(NULL), local_pred(false),
334      _dist(NULL), local_dist(false),
335      _reached(NULL), local_reached(false),
336      _processed(NULL), local_processed(false)
337    { }
338
339    ///Destructor.
340    ~Bfs()
341    {
342      if(local_pred) delete _pred;
343      if(local_dist) delete _dist;
344      if(local_reached) delete _reached;
345      if(local_processed) delete _processed;
346    }
347
348    ///Sets the map that stores the predecessor arcs.
349
350    ///Sets the map that stores the predecessor arcs.
351    ///If you don't use this function before calling \ref run(),
352    ///it will allocate one. The destructor deallocates this
353    ///automatically allocated map, of course.
354    ///\return <tt> (*this) </tt>
355    Bfs &predMap(PredMap &m)
356    {
357      if(local_pred) {
358        delete _pred;
359        local_pred=false;
360      }
361      _pred = &m;
362      return *this;
363    }
364
365    ///Sets the map that indicates which nodes are reached.
366
367    ///Sets the map that indicates which nodes are reached.
368    ///If you don't use this function before calling \ref run(),
369    ///it will allocate one. The destructor deallocates this
370    ///automatically allocated map, of course.
371    ///\return <tt> (*this) </tt>
372    Bfs &reachedMap(ReachedMap &m)
373    {
374      if(local_reached) {
375        delete _reached;
376        local_reached=false;
377      }
378      _reached = &m;
379      return *this;
380    }
381
382    ///Sets the map that indicates which nodes are processed.
383
384    ///Sets the map that indicates which nodes are processed.
385    ///If you don't use this function before calling \ref run(),
386    ///it will allocate one. The destructor deallocates this
387    ///automatically allocated map, of course.
388    ///\return <tt> (*this) </tt>
389    Bfs &processedMap(ProcessedMap &m)
390    {
391      if(local_processed) {
392        delete _processed;
393        local_processed=false;
394      }
395      _processed = &m;
396      return *this;
397    }
398
399    ///Sets the map that stores the distances of the nodes.
400
401    ///Sets the map that stores the distances of the nodes calculated by
402    ///the algorithm.
403    ///If you don't use this function before calling \ref run(),
404    ///it will allocate one. The destructor deallocates this
405    ///automatically allocated map, of course.
406    ///\return <tt> (*this) </tt>
407    Bfs &distMap(DistMap &m)
408    {
409      if(local_dist) {
410        delete _dist;
411        local_dist=false;
412      }
413      _dist = &m;
414      return *this;
415    }
416
417  public:
418
419    ///\name Execution control
420    ///The simplest way to execute the algorithm is to use
421    ///one of the member functions called \ref lemon::Bfs::run() "run()".
422    ///\n
423    ///If you need more control on the execution, first you must call
424    ///\ref lemon::Bfs::init() "init()", then you can add several source
425    ///nodes with \ref lemon::Bfs::addSource() "addSource()".
426    ///Finally \ref lemon::Bfs::start() "start()" will perform the
427    ///actual path computation.
428
429    ///@{
430
431    ///Initializes the internal data structures.
432
433    ///Initializes the internal data structures.
434    ///
435    void init()
436    {
437      create_maps();
438      _queue.resize(countNodes(*G));
439      _queue_head=_queue_tail=0;
440      _curr_dist=1;
441      for ( NodeIt u(*G) ; u!=INVALID ; ++u ) {
442        _pred->set(u,INVALID);
443        _reached->set(u,false);
444        _processed->set(u,false);
445      }
446    }
447
448    ///Adds a new source node.
449
450    ///Adds a new source node to the set of nodes to be processed.
451    ///
452    void addSource(Node s)
453    {
454      if(!(*_reached)[s])
455        {
456          _reached->set(s,true);
457          _pred->set(s,INVALID);
458          _dist->set(s,0);
459          _queue[_queue_head++]=s;
460          _queue_next_dist=_queue_head;
461        }
462    }
463
464    ///Processes the next node.
465
466    ///Processes the next node.
467    ///
468    ///\return The processed node.
469    ///
470    ///\pre The queue must not be empty.
471    Node processNextNode()
472    {
473      if(_queue_tail==_queue_next_dist) {
474        _curr_dist++;
475        _queue_next_dist=_queue_head;
476      }
477      Node n=_queue[_queue_tail++];
478      _processed->set(n,true);
479      Node m;
480      for(OutArcIt e(*G,n);e!=INVALID;++e)
481        if(!(*_reached)[m=G->target(e)]) {
482          _queue[_queue_head++]=m;
483          _reached->set(m,true);
484          _pred->set(m,e);
485          _dist->set(m,_curr_dist);
486        }
487      return n;
488    }
489
490    ///Processes the next node.
491
492    ///Processes the next node and checks if the given target node
493    ///is reached. If the target node is reachable from the processed
494    ///node, then the \c reach parameter will be set to \c true.
495    ///
496    ///\param target The target node.
497    ///\retval reach Indicates if the target node is reached.
498    ///It should be initially \c false.
499    ///
500    ///\return The processed node.
501    ///
502    ///\pre The queue must not be empty.
503    Node processNextNode(Node target, bool& reach)
504    {
505      if(_queue_tail==_queue_next_dist) {
506        _curr_dist++;
507        _queue_next_dist=_queue_head;
508      }
509      Node n=_queue[_queue_tail++];
510      _processed->set(n,true);
511      Node m;
512      for(OutArcIt e(*G,n);e!=INVALID;++e)
513        if(!(*_reached)[m=G->target(e)]) {
514          _queue[_queue_head++]=m;
515          _reached->set(m,true);
516          _pred->set(m,e);
517          _dist->set(m,_curr_dist);
518          reach = reach || (target == m);
519        }
520      return n;
521    }
522
523    ///Processes the next node.
524
525    ///Processes the next node and checks if at least one of reached
526    ///nodes has \c true value in the \c nm node map. If one node
527    ///with \c true value is reachable from the processed node, then the
528    ///\c rnode parameter will be set to the first of such nodes.
529    ///
530    ///\param nm A \c bool (or convertible) node map that indicates the
531    ///possible targets.
532    ///\retval rnode The reached target node.
533    ///It should be initially \c INVALID.
534    ///
535    ///\return The processed node.
536    ///
537    ///\pre The queue must not be empty.
538    template<class NM>
539    Node processNextNode(const NM& nm, Node& rnode)
540    {
541      if(_queue_tail==_queue_next_dist) {
542        _curr_dist++;
543        _queue_next_dist=_queue_head;
544      }
545      Node n=_queue[_queue_tail++];
546      _processed->set(n,true);
547      Node m;
548      for(OutArcIt e(*G,n);e!=INVALID;++e)
549        if(!(*_reached)[m=G->target(e)]) {
550          _queue[_queue_head++]=m;
551          _reached->set(m,true);
552          _pred->set(m,e);
553          _dist->set(m,_curr_dist);
554          if (nm[m] && rnode == INVALID) rnode = m;
555        }
556      return n;
557    }
558
559    ///The next node to be processed.
560
561    ///Returns the next node to be processed or \c INVALID if the queue
562    ///is empty.
563    Node nextNode() const
564    {
565      return _queue_tail<_queue_head?_queue[_queue_tail]:INVALID;
566    }
567
568    ///\brief Returns \c false if there are nodes
569    ///to be processed.
570    ///
571    ///Returns \c false if there are nodes
572    ///to be processed in the queue.
573    bool emptyQueue() const { return _queue_tail==_queue_head; }
574
575    ///Returns the number of the nodes to be processed.
576
577    ///Returns the number of the nodes to be processed in the queue.
578    int queueSize() const { return _queue_head-_queue_tail; }
579
580    ///Executes the algorithm.
581
582    ///Executes the algorithm.
583    ///
584    ///This method runs the %BFS algorithm from the root node(s)
585    ///in order to compute the shortest path to each node.
586    ///
587    ///The algorithm computes
588    ///- the shortest path tree (forest),
589    ///- the distance of each node from the root(s).
590    ///
591    ///\pre init() must be called and at least one root node should be
592    ///added with addSource() before using this function.
593    ///
594    ///\note <tt>b.start()</tt> is just a shortcut of the following code.
595    ///\code
596    ///  while ( !b.emptyQueue() ) {
597    ///    b.processNextNode();
598    ///  }
599    ///\endcode
600    void start()
601    {
602      while ( !emptyQueue() ) processNextNode();
603    }
604
605    ///Executes the algorithm until the given target node is reached.
606
607    ///Executes the algorithm until the given target node is reached.
608    ///
609    ///This method runs the %BFS algorithm from the root node(s)
610    ///in order to compute the shortest path to \c dest.
611    ///
612    ///The algorithm computes
613    ///- the shortest path to \c dest,
614    ///- the distance of \c dest from the root(s).
615    ///
616    ///\pre init() must be called and at least one root node should be
617    ///added with addSource() before using this function.
618    ///
619    ///\note <tt>b.start(t)</tt> is just a shortcut of the following code.
620    ///\code
621    ///  bool reach = false;
622    ///  while ( !b.emptyQueue() && !reach ) {
623    ///    b.processNextNode(t, reach);
624    ///  }
625    ///\endcode
626    void start(Node dest)
627    {
628      bool reach = false;
629      while ( !emptyQueue() && !reach ) processNextNode(dest, reach);
630    }
631
632    ///Executes the algorithm until a condition is met.
633
634    ///Executes the algorithm until a condition is met.
635    ///
636    ///This method runs the %BFS algorithm from the root node(s) in
637    ///order to compute the shortest path to a node \c v with
638    /// <tt>nm[v]</tt> true, if such a node can be found.
639    ///
640    ///\param nm A \c bool (or convertible) node map. The algorithm
641    ///will stop when it reaches a node \c v with <tt>nm[v]</tt> true.
642    ///
643    ///\return The reached node \c v with <tt>nm[v]</tt> true or
644    ///\c INVALID if no such node was found.
645    ///
646    ///\pre init() must be called and at least one root node should be
647    ///added with addSource() before using this function.
648    ///
649    ///\note <tt>b.start(nm)</tt> is just a shortcut of the following code.
650    ///\code
651    ///  Node rnode = INVALID;
652    ///  while ( !b.emptyQueue() && rnode == INVALID ) {
653    ///    b.processNextNode(nm, rnode);
654    ///  }
655    ///  return rnode;
656    ///\endcode
657    template<class NodeBoolMap>
658    Node start(const NodeBoolMap &nm)
659    {
660      Node rnode = INVALID;
661      while ( !emptyQueue() && rnode == INVALID ) {
662        processNextNode(nm, rnode);
663      }
664      return rnode;
665    }
666
667    ///Runs the algorithm from the given node.
668
669    ///This method runs the %BFS algorithm from node \c s
670    ///in order to compute the shortest path to each node.
671    ///
672    ///The algorithm computes
673    ///- the shortest path tree,
674    ///- the distance of each node from the root.
675    ///
676    ///\note <tt>b.run(s)</tt> is just a shortcut of the following code.
677    ///\code
678    ///  b.init();
679    ///  b.addSource(s);
680    ///  b.start();
681    ///\endcode
682    void run(Node s) {
683      init();
684      addSource(s);
685      start();
686    }
687
688    ///Finds the shortest path between \c s and \c t.
689
690    ///This method runs the %BFS algorithm from node \c s
691    ///in order to compute the shortest path to \c t.
692    ///
693    ///\return The length of the shortest <tt>s</tt>--<tt>t</tt> path,
694    ///if \c t is reachable form \c s, \c 0 otherwise.
695    ///
696    ///\note Apart from the return value, <tt>b.run(s,t)</tt> is just a
697    ///shortcut of the following code.
698    ///\code
699    ///  b.init();
700    ///  b.addSource(s);
701    ///  b.start(t);
702    ///\endcode
703    int run(Node s,Node t) {
704      init();
705      addSource(s);
706      start(t);
707      return reached(t) ? _curr_dist : 0;
708    }
709
710    ///Runs the algorithm to visit all nodes in the digraph.
711
712    ///This method runs the %BFS algorithm in order to
713    ///compute the shortest path to each node.
714    ///
715    ///The algorithm computes
716    ///- the shortest path tree (forest),
717    ///- the distance of each node from the root(s).
718    ///
719    ///\note <tt>b.run(s)</tt> is just a shortcut of the following code.
720    ///\code
721    ///  b.init();
722    ///  for (NodeIt n(gr); n != INVALID; ++n) {
723    ///    if (!b.reached(n)) {
724    ///      b.addSource(n);
725    ///      b.start();
726    ///    }
727    ///  }
728    ///\endcode
729    void run() {
730      init();
731      for (NodeIt n(*G); n != INVALID; ++n) {
732        if (!reached(n)) {
733          addSource(n);
734          start();
735        }
736      }
737    }
738
739    ///@}
740
741    ///\name Query Functions
742    ///The result of the %BFS algorithm can be obtained using these
743    ///functions.\n
744    ///Either \ref lemon::Bfs::run() "run()" or \ref lemon::Bfs::start()
745    ///"start()" must be called before using them.
746
747    ///@{
748
749    ///The shortest path to a node.
750
751    ///Returns the shortest path to a node.
752    ///
753    ///\warning \c t should be reachable from the root(s).
754    ///
755    ///\pre Either \ref run() or \ref start() must be called before
756    ///using this function.
757    Path path(Node t) const { return Path(*G, *_pred, t); }
758
759    ///The distance of a node from the root(s).
760
761    ///Returns the distance of a node from the root(s).
762    ///
763    ///\warning If node \c v is not reachable from the root(s), then
764    ///the return value of this function is undefined.
765    ///
766    ///\pre Either \ref run() or \ref start() must be called before
767    ///using this function.
768    int dist(Node v) const { return (*_dist)[v]; }
769
770    ///Returns the 'previous arc' of the shortest path tree for a node.
771
772    ///This function returns the 'previous arc' of the shortest path
773    ///tree for the node \c v, i.e. it returns the last arc of a
774    ///shortest path from the root(s) to \c v. It is \c INVALID if \c v
775    ///is not reachable from the root(s) or if \c v is a root.
776    ///
777    ///The shortest path tree used here is equal to the shortest path
778    ///tree used in \ref predNode().
779    ///
780    ///\pre Either \ref run() or \ref start() must be called before
781    ///using this function.
782    Arc predArc(Node v) const { return (*_pred)[v];}
783
784    ///Returns the 'previous node' of the shortest path tree for a node.
785
786    ///This function returns the 'previous node' of the shortest path
787    ///tree for the node \c v, i.e. it returns the last but one node
788    ///from a shortest path from the root(s) to \c v. It is \c INVALID
789    ///if \c v is not reachable from the root(s) or if \c v is a root.
790    ///
791    ///The shortest path tree used here is equal to the shortest path
792    ///tree used in \ref predArc().
793    ///
794    ///\pre Either \ref run() or \ref start() must be called before
795    ///using this function.
796    Node predNode(Node v) const { return (*_pred)[v]==INVALID ? INVALID:
797                                  G->source((*_pred)[v]); }
798
799    ///\brief Returns a const reference to the node map that stores the
800    /// distances of the nodes.
801    ///
802    ///Returns a const reference to the node map that stores the distances
803    ///of the nodes calculated by the algorithm.
804    ///
805    ///\pre Either \ref run() or \ref init()
806    ///must be called before using this function.
807    const DistMap &distMap() const { return *_dist;}
808
809    ///\brief Returns a const reference to the node map that stores the
810    ///predecessor arcs.
811    ///
812    ///Returns a const reference to the node map that stores the predecessor
813    ///arcs, which form the shortest path tree.
814    ///
815    ///\pre Either \ref run() or \ref init()
816    ///must be called before using this function.
817    const PredMap &predMap() const { return *_pred;}
818
819    ///Checks if a node is reachable from the root(s).
820
821    ///Returns \c true if \c v is reachable from the root(s).
822    ///\pre Either \ref run() or \ref start()
823    ///must be called before using this function.
824    bool reached(Node v) const { return (*_reached)[v]; }
825
826    ///@}
827  };
828
829  ///Default traits class of bfs() function.
830
831  ///Default traits class of bfs() function.
832  ///\tparam GR Digraph type.
833  template<class GR>
834  struct BfsWizardDefaultTraits
835  {
836    ///The type of the digraph the algorithm runs on.
837    typedef GR Digraph;
838
839    ///\brief The type of the map that stores the predecessor
840    ///arcs of the shortest paths.
841    ///
842    ///The type of the map that stores the predecessor
843    ///arcs of the shortest paths.
844    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
845    typedef NullMap<typename Digraph::Node,typename Digraph::Arc> PredMap;
846    ///Instantiates a \ref PredMap.
847
848    ///This function instantiates a \ref PredMap.
849    ///\param g is the digraph, to which we would like to define the
850    ///\ref PredMap.
851    ///\todo The digraph alone may be insufficient to initialize
852#ifdef DOXYGEN
853    static PredMap *createPredMap(const Digraph &g)
854#else
855    static PredMap *createPredMap(const Digraph &)
856#endif
857    {
858      return new PredMap();
859    }
860
861    ///The type of the map that indicates which nodes are processed.
862
863    ///The type of the map that indicates which nodes are processed.
864    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
865    typedef NullMap<typename Digraph::Node,bool> ProcessedMap;
866    ///Instantiates a \ref ProcessedMap.
867
868    ///This function instantiates a \ref ProcessedMap.
869    ///\param g is the digraph, to which
870    ///we would like to define the \ref ProcessedMap.
871#ifdef DOXYGEN
872    static ProcessedMap *createProcessedMap(const Digraph &g)
873#else
874    static ProcessedMap *createProcessedMap(const Digraph &)
875#endif
876    {
877      return new ProcessedMap();
878    }
879
880    ///The type of the map that indicates which nodes are reached.
881
882    ///The type of the map that indicates which nodes are reached.
883    ///It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
884    typedef typename Digraph::template NodeMap<bool> ReachedMap;
885    ///Instantiates a \ref ReachedMap.
886
887    ///This function instantiates a \ref ReachedMap.
888    ///\param g is the digraph, to which
889    ///we would like to define the \ref ReachedMap.
890    static ReachedMap *createReachedMap(const Digraph &g)
891    {
892      return new ReachedMap(g);
893    }
894
895    ///The type of the map that stores the distances of the nodes.
896
897    ///The type of the map that stores the distances of the nodes.
898    ///It must meet the \ref concepts::WriteMap "WriteMap" concept.
899    ///
900    typedef NullMap<typename Digraph::Node,int> DistMap;
901    ///Instantiates a \ref DistMap.
902
903    ///This function instantiates a \ref DistMap.
904    ///\param g is the digraph, to which we would like to define
905    ///the \ref DistMap
906#ifdef DOXYGEN
907    static DistMap *createDistMap(const Digraph &g)
908#else
909    static DistMap *createDistMap(const Digraph &)
910#endif
911    {
912      return new DistMap();
913    }
914  };
915
916  /// Default traits class used by \ref BfsWizard
917
918  /// To make it easier to use Bfs algorithm
919  /// we have created a wizard class.
920  /// This \ref BfsWizard class needs default traits,
921  /// as well as the \ref Bfs class.
922  /// The \ref BfsWizardBase is a class to be the default traits of the
923  /// \ref BfsWizard class.
924  template<class GR>
925  class BfsWizardBase : public BfsWizardDefaultTraits<GR>
926  {
927
928    typedef BfsWizardDefaultTraits<GR> Base;
929  protected:
930    //The type of the nodes in the digraph.
931    typedef typename Base::Digraph::Node Node;
932
933    //Pointer to the digraph the algorithm runs on.
934    void *_g;
935    //Pointer to the map of reached nodes.
936    void *_reached;
937    //Pointer to the map of processed nodes.
938    void *_processed;
939    //Pointer to the map of predecessors arcs.
940    void *_pred;
941    //Pointer to the map of distances.
942    void *_dist;
943    //Pointer to the source node.
944    Node _source;
945
946    public:
947    /// Constructor.
948
949    /// This constructor does not require parameters, therefore it initiates
950    /// all of the attributes to default values (0, INVALID).
951    BfsWizardBase() : _g(0), _reached(0), _processed(0), _pred(0),
952                      _dist(0), _source(INVALID) {}
953
954    /// Constructor.
955
956    /// This constructor requires some parameters,
957    /// listed in the parameters list.
958    /// Others are initiated to 0.
959    /// \param g The digraph the algorithm runs on.
960    /// \param s The source node.
961    BfsWizardBase(const GR &g, Node s=INVALID) :
962      _g(reinterpret_cast<void*>(const_cast<GR*>(&g))),
963      _reached(0), _processed(0), _pred(0), _dist(0), _source(s) {}
964
965  };
966
967  /// Auxiliary class for the function type interface of BFS algorithm.
968
969  /// This auxiliary class is created to implement the function type
970  /// interface of \ref Bfs algorithm. It uses the functions and features
971  /// of the plain \ref Bfs, but it is much simpler to use it.
972  /// It should only be used through the \ref bfs() function, which makes
973  /// it easier to use the algorithm.
974  ///
975  /// Simplicity means that the way to change the types defined
976  /// in the traits class is based on functions that returns the new class
977  /// and not on templatable built-in classes.
978  /// When using the plain \ref Bfs
979  /// the new class with the modified type comes from
980  /// the original class by using the ::
981  /// operator. In the case of \ref BfsWizard only
982  /// a function have to be called, and it will
983  /// return the needed class.
984  ///
985  /// It does not have own \ref run() method. When its \ref run() method
986  /// is called, it initiates a plain \ref Bfs object, and calls the
987  /// \ref Bfs::run() method of it.
988  template<class TR>
989  class BfsWizard : public TR
990  {
991    typedef TR Base;
992
993    ///The type of the digraph the algorithm runs on.
994    typedef typename TR::Digraph Digraph;
995
996    typedef typename Digraph::Node Node;
997    typedef typename Digraph::NodeIt NodeIt;
998    typedef typename Digraph::Arc Arc;
999    typedef typename Digraph::OutArcIt OutArcIt;
1000
1001    ///\brief The type of the map that stores the predecessor
1002    ///arcs of the shortest paths.
1003    typedef typename TR::PredMap PredMap;
1004    ///\brief The type of the map that stores the distances of the nodes.
1005    typedef typename TR::DistMap DistMap;
1006    ///\brief The type of the map that indicates which nodes are reached.
1007    typedef typename TR::ReachedMap ReachedMap;
1008    ///\brief The type of the map that indicates which nodes are processed.
1009    typedef typename TR::ProcessedMap ProcessedMap;
1010
1011  public:
1012
1013    /// Constructor.
1014    BfsWizard() : TR() {}
1015
1016    /// Constructor that requires parameters.
1017
1018    /// Constructor that requires parameters.
1019    /// These parameters will be the default values for the traits class.
1020    BfsWizard(const Digraph &g, Node s=INVALID) :
1021      TR(g,s) {}
1022
1023    ///Copy constructor
1024    BfsWizard(const TR &b) : TR(b) {}
1025
1026    ~BfsWizard() {}
1027
1028    ///Runs BFS algorithm from a source node.
1029
1030    ///Runs BFS algorithm from a source node.
1031    ///The node can be given with the \ref source() function.
1032    void run()
1033    {
1034      if(Base::_source==INVALID) throw UninitializedParameter();
1035      Bfs<Digraph,TR> alg(*reinterpret_cast<const Digraph*>(Base::_g));
1036      if(Base::_reached)
1037        alg.reachedMap(*reinterpret_cast<ReachedMap*>(Base::_reached));
1038      if(Base::_processed)
1039        alg.processedMap(*reinterpret_cast<ProcessedMap*>(Base::_processed));
1040      if(Base::_pred)
1041        alg.predMap(*reinterpret_cast<PredMap*>(Base::_pred));
1042      if(Base::_dist)
1043        alg.distMap(*reinterpret_cast<DistMap*>(Base::_dist));
1044      alg.run(Base::_source);
1045    }
1046
1047    ///Runs BFS algorithm from the given node.
1048
1049    ///Runs BFS algorithm from the given node.
1050    ///\param s is the given source.
1051    void run(Node s)
1052    {
1053      Base::_source=s;
1054      run();
1055    }
1056
1057    /// Sets the source node, from which the Bfs algorithm runs.
1058
1059    /// Sets the source node, from which the Bfs algorithm runs.
1060    /// \param s is the source node.
1061    BfsWizard<TR> &source(Node s)
1062    {
1063      Base::_source=s;
1064      return *this;
1065    }
1066
1067    template<class T>
1068    struct DefPredMapBase : public Base {
1069      typedef T PredMap;
1070      static PredMap *createPredMap(const Digraph &) { return 0; };
1071      DefPredMapBase(const TR &b) : TR(b) {}
1072    };
1073    ///\brief \ref named-templ-param "Named parameter"
1074    ///for setting \ref PredMap object.
1075    ///
1076    /// \ref named-templ-param "Named parameter"
1077    ///for setting \ref PredMap object.
1078    template<class T>
1079    BfsWizard<DefPredMapBase<T> > predMap(const T &t)
1080    {
1081      Base::_pred=reinterpret_cast<void*>(const_cast<T*>(&t));
1082      return BfsWizard<DefPredMapBase<T> >(*this);
1083    }
1084
1085    template<class T>
1086    struct DefReachedMapBase : public Base {
1087      typedef T ReachedMap;
1088      static ReachedMap *createReachedMap(const Digraph &) { return 0; };
1089      DefReachedMapBase(const TR &b) : TR(b) {}
1090    };
1091    ///\brief \ref named-templ-param "Named parameter"
1092    ///for setting \ref ReachedMap object.
1093    ///
1094    /// \ref named-templ-param "Named parameter"
1095    ///for setting \ref ReachedMap object.
1096    template<class T>
1097    BfsWizard<DefReachedMapBase<T> > reachedMap(const T &t)
1098    {
1099      Base::_reached=reinterpret_cast<void*>(const_cast<T*>(&t));
1100      return BfsWizard<DefReachedMapBase<T> >(*this);
1101    }
1102
1103    template<class T>
1104    struct DefProcessedMapBase : public Base {
1105      typedef T ProcessedMap;
1106      static ProcessedMap *createProcessedMap(const Digraph &) { return 0; };
1107      DefProcessedMapBase(const TR &b) : TR(b) {}
1108    };
1109    ///\brief \ref named-templ-param "Named parameter"
1110    ///for setting \ref ProcessedMap object.
1111    ///
1112    /// \ref named-templ-param "Named parameter"
1113    ///for setting \ref ProcessedMap object.
1114    template<class T>
1115    BfsWizard<DefProcessedMapBase<T> > processedMap(const T &t)
1116    {
1117      Base::_processed=reinterpret_cast<void*>(const_cast<T*>(&t));
1118      return BfsWizard<DefProcessedMapBase<T> >(*this);
1119    }
1120
1121    template<class T>
1122    struct DefDistMapBase : public Base {
1123      typedef T DistMap;
1124      static DistMap *createDistMap(const Digraph &) { return 0; };
1125      DefDistMapBase(const TR &b) : TR(b) {}
1126    };
1127    ///\brief \ref named-templ-param "Named parameter"
1128    ///for setting \ref DistMap object.
1129    ///
1130    /// \ref named-templ-param "Named parameter"
1131    ///for setting \ref DistMap object.
1132    template<class T>
1133    BfsWizard<DefDistMapBase<T> > distMap(const T &t)
1134    {
1135      Base::_dist=reinterpret_cast<void*>(const_cast<T*>(&t));
1136      return BfsWizard<DefDistMapBase<T> >(*this);
1137    }
1138
1139  };
1140
1141  ///Function type interface for Bfs algorithm.
1142
1143  /// \ingroup search
1144  ///Function type interface for Bfs algorithm.
1145  ///
1146  ///This function also has several
1147  ///\ref named-templ-func-param "named parameters",
1148  ///they are declared as the members of class \ref BfsWizard.
1149  ///The following
1150  ///example shows how to use these parameters.
1151  ///\code
1152  ///  bfs(g,source).predMap(preds).run();
1153  ///\endcode
1154  ///\warning Don't forget to put the \ref BfsWizard::run() "run()"
1155  ///to the end of the parameter list.
1156  ///\sa BfsWizard
1157  ///\sa Bfs
1158  template<class GR>
1159  BfsWizard<BfsWizardBase<GR> >
1160  bfs(const GR &g,typename GR::Node s=INVALID)
1161  {
1162    return BfsWizard<BfsWizardBase<GR> >(g,s);
1163  }
1164
1165#ifdef DOXYGEN
1166  /// \brief Visitor class for BFS.
1167  ///
1168  /// This class defines the interface of the BfsVisit events, and
1169  /// it could be the base of a real visitor class.
1170  template <typename _Digraph>
1171  struct BfsVisitor {
1172    typedef _Digraph Digraph;
1173    typedef typename Digraph::Arc Arc;
1174    typedef typename Digraph::Node Node;
1175    /// \brief Called for the source node(s) of the BFS.
1176    ///
1177    /// This function is called for the source node(s) of the BFS.
1178    void start(const Node& node) {}
1179    /// \brief Called when a node is reached first time.
1180    ///
1181    /// This function is called when a node is reached first time.
1182    void reach(const Node& node) {}
1183    /// \brief Called when a node is processed.
1184    ///
1185    /// This function is called when a node is processed.
1186    void process(const Node& node) {}
1187    /// \brief Called when an arc reaches a new node.
1188    ///
1189    /// This function is called when the BFS finds an arc whose target node
1190    /// is not reached yet.
1191    void discover(const Arc& arc) {}
1192    /// \brief Called when an arc is examined but its target node is
1193    /// already discovered.
1194    ///
1195    /// This function is called when an arc is examined but its target node is
1196    /// already discovered.
1197    void examine(const Arc& arc) {}
1198  };
1199#else
1200  template <typename _Digraph>
1201  struct BfsVisitor {
1202    typedef _Digraph Digraph;
1203    typedef typename Digraph::Arc Arc;
1204    typedef typename Digraph::Node Node;
1205    void start(const Node&) {}
1206    void reach(const Node&) {}
1207    void process(const Node&) {}
1208    void discover(const Arc&) {}
1209    void examine(const Arc&) {}
1210
1211    template <typename _Visitor>
1212    struct Constraints {
1213      void constraints() {
1214        Arc arc;
1215        Node node;
1216        visitor.start(node);
1217        visitor.reach(node);
1218        visitor.process(node);
1219        visitor.discover(arc);
1220        visitor.examine(arc);
1221      }
1222      _Visitor& visitor;
1223    };
1224  };
1225#endif
1226
1227  /// \brief Default traits class of BfsVisit class.
1228  ///
1229  /// Default traits class of BfsVisit class.
1230  /// \tparam _Digraph The type of the digraph the algorithm runs on.
1231  template<class _Digraph>
1232  struct BfsVisitDefaultTraits {
1233
1234    /// \brief The type of the digraph the algorithm runs on.
1235    typedef _Digraph Digraph;
1236
1237    /// \brief The type of the map that indicates which nodes are reached.
1238    ///
1239    /// The type of the map that indicates which nodes are reached.
1240    /// It must meet the \ref concepts::ReadWriteMap "ReadWriteMap" concept.
1241    typedef typename Digraph::template NodeMap<bool> ReachedMap;
1242
1243    /// \brief Instantiates a \ref ReachedMap.
1244    ///
1245    /// This function instantiates a \ref ReachedMap.
1246    /// \param digraph is the digraph, to which
1247    /// we would like to define the \ref ReachedMap.
1248    static ReachedMap *createReachedMap(const Digraph &digraph) {
1249      return new ReachedMap(digraph);
1250    }
1251
1252  };
1253
1254  /// \ingroup search
1255  ///
1256  /// \brief %BFS algorithm class with visitor interface.
1257  ///
1258  /// This class provides an efficient implementation of the %BFS algorithm
1259  /// with visitor interface.
1260  ///
1261  /// The %BfsVisit class provides an alternative interface to the Bfs
1262  /// class. It works with callback mechanism, the BfsVisit object calls
1263  /// the member functions of the \c Visitor class on every BFS event.
1264  ///
1265  /// \tparam _Digraph The type of the digraph the algorithm runs on.
1266  /// The default value is
1267  /// \ref ListDigraph. The value of _Digraph is not used directly by
1268  /// \ref BfsVisit, it is only passed to \ref BfsVisitDefaultTraits.
1269  /// \tparam _Visitor The Visitor type that is used by the algorithm.
1270  /// \ref BfsVisitor "BfsVisitor<_Digraph>" is an empty visitor, which
1271  /// does not observe the BFS events. If you want to observe the BFS
1272  /// events, you should implement your own visitor class.
1273  /// \tparam _Traits Traits class to set various data types used by the
1274  /// algorithm. The default traits class is
1275  /// \ref BfsVisitDefaultTraits "BfsVisitDefaultTraits<_Digraph>".
1276  /// See \ref BfsVisitDefaultTraits for the documentation of
1277  /// a BFS visit traits class.
1278#ifdef DOXYGEN
1279  template <typename _Digraph, typename _Visitor, typename _Traits>
1280#else
1281  template <typename _Digraph = ListDigraph,
1282            typename _Visitor = BfsVisitor<_Digraph>,
1283            typename _Traits = BfsDefaultTraits<_Digraph> >
1284#endif
1285  class BfsVisit {
1286  public:
1287
1288    /// \brief \ref Exception for uninitialized parameters.
1289    ///
1290    /// This error represents problems in the initialization
1291    /// of the parameters of the algorithm.
1292    class UninitializedParameter : public lemon::UninitializedParameter {
1293    public:
1294      virtual const char* what() const throw()
1295      {
1296        return "lemon::BfsVisit::UninitializedParameter";
1297      }
1298    };
1299
1300    ///The traits class.
1301    typedef _Traits Traits;
1302
1303    ///The type of the digraph the algorithm runs on.
1304    typedef typename Traits::Digraph Digraph;
1305
1306    ///The visitor type used by the algorithm.
1307    typedef _Visitor Visitor;
1308
1309    ///The type of the map that indicates which nodes are reached.
1310    typedef typename Traits::ReachedMap ReachedMap;
1311
1312  private:
1313
1314    typedef typename Digraph::Node Node;
1315    typedef typename Digraph::NodeIt NodeIt;
1316    typedef typename Digraph::Arc Arc;
1317    typedef typename Digraph::OutArcIt OutArcIt;
1318
1319    //Pointer to the underlying digraph.
1320    const Digraph *_digraph;
1321    //Pointer to the visitor object.
1322    Visitor *_visitor;
1323    //Pointer to the map of reached status of the nodes.
1324    ReachedMap *_reached;
1325    //Indicates if _reached is locally allocated (true) or not.
1326    bool local_reached;
1327
1328    std::vector<typename Digraph::Node> _list;
1329    int _list_front, _list_back;
1330
1331    ///Creates the maps if necessary.
1332    ///\todo Better memory allocation (instead of new).
1333    void create_maps() {
1334      if(!_reached) {
1335        local_reached = true;
1336        _reached = Traits::createReachedMap(*_digraph);
1337      }
1338    }
1339
1340  protected:
1341
1342    BfsVisit() {}
1343
1344  public:
1345
1346    typedef BfsVisit Create;
1347
1348    /// \name Named template parameters
1349
1350    ///@{
1351    template <class T>
1352    struct DefReachedMapTraits : public Traits {
1353      typedef T ReachedMap;
1354      static ReachedMap *createReachedMap(const Digraph &digraph) {
1355        throw UninitializedParameter();
1356      }
1357    };
1358    /// \brief \ref named-templ-param "Named parameter" for setting
1359    /// ReachedMap type.
1360    ///
1361    /// \ref named-templ-param "Named parameter" for setting ReachedMap type.
1362    template <class T>
1363    struct DefReachedMap : public BfsVisit< Digraph, Visitor,
1364                                            DefReachedMapTraits<T> > {
1365      typedef BfsVisit< Digraph, Visitor, DefReachedMapTraits<T> > Create;
1366    };
1367    ///@}
1368
1369  public:
1370
1371    /// \brief Constructor.
1372    ///
1373    /// Constructor.
1374    ///
1375    /// \param digraph The digraph the algorithm runs on.
1376    /// \param visitor The visitor object of the algorithm.
1377    BfsVisit(const Digraph& digraph, Visitor& visitor)
1378      : _digraph(&digraph), _visitor(&visitor),
1379        _reached(0), local_reached(false) {}
1380
1381    /// \brief Destructor.
1382    ~BfsVisit() {
1383      if(local_reached) delete _reached;
1384    }
1385
1386    /// \brief Sets the map that indicates which nodes are reached.
1387    ///
1388    /// Sets the map that indicates which nodes are reached.
1389    /// If you don't use this function before calling \ref run(),
1390    /// it will allocate one. The destructor deallocates this
1391    /// automatically allocated map, of course.
1392    /// \return <tt> (*this) </tt>
1393    BfsVisit &reachedMap(ReachedMap &m) {
1394      if(local_reached) {
1395        delete _reached;
1396        local_reached = false;
1397      }
1398      _reached = &m;
1399      return *this;
1400    }
1401
1402  public:
1403
1404    /// \name Execution control
1405    /// The simplest way to execute the algorithm is to use
1406    /// one of the member functions called \ref lemon::BfsVisit::run()
1407    /// "run()".
1408    /// \n
1409    /// If you need more control on the execution, first you must call
1410    /// \ref lemon::BfsVisit::init() "init()", then you can add several
1411    /// source nodes with \ref lemon::BfsVisit::addSource() "addSource()".
1412    /// Finally \ref lemon::BfsVisit::start() "start()" will perform the
1413    /// actual path computation.
1414
1415    /// @{
1416
1417    /// \brief Initializes the internal data structures.
1418    ///
1419    /// Initializes the internal data structures.
1420    void init() {
1421      create_maps();
1422      _list.resize(countNodes(*_digraph));
1423      _list_front = _list_back = -1;
1424      for (NodeIt u(*_digraph) ; u != INVALID ; ++u) {
1425        _reached->set(u, false);
1426      }
1427    }
1428
1429    /// \brief Adds a new source node.
1430    ///
1431    /// Adds a new source node to the set of nodes to be processed.
1432    void addSource(Node s) {
1433      if(!(*_reached)[s]) {
1434          _reached->set(s,true);
1435          _visitor->start(s);
1436          _visitor->reach(s);
1437          _list[++_list_back] = s;
1438        }
1439    }
1440
1441    /// \brief Processes the next node.
1442    ///
1443    /// Processes the next node.
1444    ///
1445    /// \return The processed node.
1446    ///
1447    /// \pre The queue must not be empty.
1448    Node processNextNode() {
1449      Node n = _list[++_list_front];
1450      _visitor->process(n);
1451      Arc e;
1452      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
1453        Node m = _digraph->target(e);
1454        if (!(*_reached)[m]) {
1455          _visitor->discover(e);
1456          _visitor->reach(m);
1457          _reached->set(m, true);
1458          _list[++_list_back] = m;
1459        } else {
1460          _visitor->examine(e);
1461        }
1462      }
1463      return n;
1464    }
1465
1466    /// \brief Processes the next node.
1467    ///
1468    /// Processes the next node and checks if the given target node
1469    /// is reached. If the target node is reachable from the processed
1470    /// node, then the \c reach parameter will be set to \c true.
1471    ///
1472    /// \param target The target node.
1473    /// \retval reach Indicates if the target node is reached.
1474    /// It should be initially \c false.
1475    ///
1476    /// \return The processed node.
1477    ///
1478    /// \pre The queue must not be empty.
1479    Node processNextNode(Node target, bool& reach) {
1480      Node n = _list[++_list_front];
1481      _visitor->process(n);
1482      Arc e;
1483      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
1484        Node m = _digraph->target(e);
1485        if (!(*_reached)[m]) {
1486          _visitor->discover(e);
1487          _visitor->reach(m);
1488          _reached->set(m, true);
1489          _list[++_list_back] = m;
1490          reach = reach || (target == m);
1491        } else {
1492          _visitor->examine(e);
1493        }
1494      }
1495      return n;
1496    }
1497
1498    /// \brief Processes the next node.
1499    ///
1500    /// Processes the next node and checks if at least one of reached
1501    /// nodes has \c true value in the \c nm node map. If one node
1502    /// with \c true value is reachable from the processed node, then the
1503    /// \c rnode parameter will be set to the first of such nodes.
1504    ///
1505    /// \param nm A \c bool (or convertible) node map that indicates the
1506    /// possible targets.
1507    /// \retval rnode The reached target node.
1508    /// It should be initially \c INVALID.
1509    ///
1510    /// \return The processed node.
1511    ///
1512    /// \pre The queue must not be empty.
1513    template <typename NM>
1514    Node processNextNode(const NM& nm, Node& rnode) {
1515      Node n = _list[++_list_front];
1516      _visitor->process(n);
1517      Arc e;
1518      for (_digraph->firstOut(e, n); e != INVALID; _digraph->nextOut(e)) {
1519        Node m = _digraph->target(e);
1520        if (!(*_reached)[m]) {
1521          _visitor->discover(e);
1522          _visitor->reach(m);
1523          _reached->set(m, true);
1524          _list[++_list_back] = m;
1525          if (nm[m] && rnode == INVALID) rnode = m;
1526        } else {
1527          _visitor->examine(e);
1528        }
1529      }
1530      return n;
1531    }
1532
1533    /// \brief The next node to be processed.
1534    ///
1535    /// Returns the next node to be processed or \c INVALID if the queue
1536    /// is empty.
1537    Node nextNode() const {
1538      return _list_front != _list_back ? _list[_list_front + 1] : INVALID;
1539    }
1540
1541    /// \brief Returns \c false if there are nodes
1542    /// to be processed.
1543    ///
1544    /// Returns \c false if there are nodes
1545    /// to be processed in the queue.
1546    bool emptyQueue() const { return _list_front == _list_back; }
1547
1548    /// \brief Returns the number of the nodes to be processed.
1549    ///
1550    /// Returns the number of the nodes to be processed in the queue.
1551    int queueSize() const { return _list_back - _list_front; }
1552
1553    /// \brief Executes the algorithm.
1554    ///
1555    /// Executes the algorithm.
1556    ///
1557    /// This method runs the %BFS algorithm from the root node(s)
1558    /// in order to compute the shortest path to each node.
1559    ///
1560    /// The algorithm computes
1561    /// - the shortest path tree (forest),
1562    /// - the distance of each node from the root(s).
1563    ///
1564    /// \pre init() must be called and at least one root node should be added
1565    /// with addSource() before using this function.
1566    ///
1567    /// \note <tt>b.start()</tt> is just a shortcut of the following code.
1568    /// \code
1569    ///   while ( !b.emptyQueue() ) {
1570    ///     b.processNextNode();
1571    ///   }
1572    /// \endcode
1573    void start() {
1574      while ( !emptyQueue() ) processNextNode();
1575    }
1576
1577    /// \brief Executes the algorithm until the given target node is reached.
1578    ///
1579    /// Executes the algorithm until the given target node is reached.
1580    ///
1581    /// This method runs the %BFS algorithm from the root node(s)
1582    /// in order to compute the shortest path to \c dest.
1583    ///
1584    /// The algorithm computes
1585    /// - the shortest path to \c dest,
1586    /// - the distance of \c dest from the root(s).
1587    ///
1588    /// \pre init() must be called and at least one root node should be
1589    /// added with addSource() before using this function.
1590    ///
1591    /// \note <tt>b.start(t)</tt> is just a shortcut of the following code.
1592    /// \code
1593    ///   bool reach = false;
1594    ///   while ( !b.emptyQueue() && !reach ) {
1595    ///     b.processNextNode(t, reach);
1596    ///   }
1597    /// \endcode
1598    void start(Node dest) {
1599      bool reach = false;
1600      while ( !emptyQueue() && !reach ) processNextNode(dest, reach);
1601    }
1602
1603    /// \brief Executes the algorithm until a condition is met.
1604    ///
1605    /// Executes the algorithm until a condition is met.
1606    ///
1607    /// This method runs the %BFS algorithm from the root node(s) in
1608    /// order to compute the shortest path to a node \c v with
1609    /// <tt>nm[v]</tt> true, if such a node can be found.
1610    ///
1611    /// \param nm must be a bool (or convertible) node map. The
1612    /// algorithm will stop when it reaches a node \c v with
1613    /// <tt>nm[v]</tt> true.
1614    ///
1615    /// \return The reached node \c v with <tt>nm[v]</tt> true or
1616    /// \c INVALID if no such node was found.
1617    ///
1618    /// \pre init() must be called and at least one root node should be
1619    /// added with addSource() before using this function.
1620    ///
1621    /// \note <tt>b.start(nm)</tt> is just a shortcut of the following code.
1622    /// \code
1623    ///   Node rnode = INVALID;
1624    ///   while ( !b.emptyQueue() && rnode == INVALID ) {
1625    ///     b.processNextNode(nm, rnode);
1626    ///   }
1627    ///   return rnode;
1628    /// \endcode
1629    template <typename NM>
1630    Node start(const NM &nm) {
1631      Node rnode = INVALID;
1632      while ( !emptyQueue() && rnode == INVALID ) {
1633        processNextNode(nm, rnode);
1634      }
1635      return rnode;
1636    }
1637
1638    /// \brief Runs the algorithm from the given node.
1639    ///
1640    /// This method runs the %BFS algorithm from node \c s
1641    /// in order to compute the shortest path to each node.
1642    ///
1643    /// The algorithm computes
1644    /// - the shortest path tree,
1645    /// - the distance of each node from the root.
1646    ///
1647    /// \note <tt>b.run(s)</tt> is just a shortcut of the following code.
1648    ///\code
1649    ///   b.init();
1650    ///   b.addSource(s);
1651    ///   b.start();
1652    ///\endcode
1653    void run(Node s) {
1654      init();
1655      addSource(s);
1656      start();
1657    }
1658
1659    /// \brief Runs the algorithm to visit all nodes in the digraph.
1660    ///
1661    /// This method runs the %BFS algorithm in order to
1662    /// compute the shortest path to each node.
1663    ///
1664    /// The algorithm computes
1665    /// - the shortest path tree (forest),
1666    /// - the distance of each node from the root(s).
1667    ///
1668    /// \note <tt>b.run(s)</tt> is just a shortcut of the following code.
1669    ///\code
1670    ///  b.init();
1671    ///  for (NodeIt n(gr); n != INVALID; ++n) {
1672    ///    if (!b.reached(n)) {
1673    ///      b.addSource(n);
1674    ///      b.start();
1675    ///    }
1676    ///  }
1677    ///\endcode
1678    void run() {
1679      init();
1680      for (NodeIt it(*_digraph); it != INVALID; ++it) {
1681        if (!reached(it)) {
1682          addSource(it);
1683          start();
1684        }
1685      }
1686    }
1687
1688    ///@}
1689
1690    /// \name Query Functions
1691    /// The result of the %BFS algorithm can be obtained using these
1692    /// functions.\n
1693    /// Either \ref lemon::BfsVisit::run() "run()" or
1694    /// \ref lemon::BfsVisit::start() "start()" must be called before
1695    /// using them.
1696    ///@{
1697
1698    /// \brief Checks if a node is reachable from the root(s).
1699    ///
1700    /// Returns \c true if \c v is reachable from the root(s).
1701    /// \pre Either \ref run() or \ref start()
1702    /// must be called before using this function.
1703    bool reached(Node v) { return (*_reached)[v]; }
1704
1705    ///@}
1706
1707  };
1708
1709} //END OF NAMESPACE LEMON
1710
1711#endif
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