COIN-OR::LEMON - Graph Library

source: lemon-1.2/lemon/smart_graph.h @ 603:425cc8328c0e

Last change on this file since 603:425cc8328c0e was 440:88ed40ad0d4f, checked in by Alpar Juttner <alpar@…>, 11 years ago

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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_SMART_GRAPH_H
20#define LEMON_SMART_GRAPH_H
21
22///\ingroup graphs
23///\file
24///\brief SmartDigraph and SmartGraph classes.
25
26#include <vector>
27
28#include <lemon/core.h>
29#include <lemon/error.h>
30#include <lemon/bits/graph_extender.h>
31
32namespace lemon {
33
34  class SmartDigraph;
35  ///Base of SmartDigraph
36
37  ///Base of SmartDigraph
38  ///
39  class SmartDigraphBase {
40  protected:
41
42    struct NodeT
43    {
44      int first_in, first_out;
45      NodeT() {}
46    };
47    struct ArcT
48    {
49      int target, source, next_in, next_out;
50      ArcT() {}
51    };
52
53    std::vector<NodeT> nodes;
54    std::vector<ArcT> arcs;
55
56  public:
57
58    typedef SmartDigraphBase Graph;
59
60    class Node;
61    class Arc;
62
63  public:
64
65    SmartDigraphBase() : nodes(), arcs() { }
66    SmartDigraphBase(const SmartDigraphBase &_g)
67      : nodes(_g.nodes), arcs(_g.arcs) { }
68
69    typedef True NodeNumTag;
70    typedef True ArcNumTag;
71
72    int nodeNum() const { return nodes.size(); }
73    int arcNum() const { return arcs.size(); }
74
75    int maxNodeId() const { return nodes.size()-1; }
76    int maxArcId() const { return arcs.size()-1; }
77
78    Node addNode() {
79      int n = nodes.size();
80      nodes.push_back(NodeT());
81      nodes[n].first_in = -1;
82      nodes[n].first_out = -1;
83      return Node(n);
84    }
85
86    Arc addArc(Node u, Node v) {
87      int n = arcs.size();
88      arcs.push_back(ArcT());
89      arcs[n].source = u._id;
90      arcs[n].target = v._id;
91      arcs[n].next_out = nodes[u._id].first_out;
92      arcs[n].next_in = nodes[v._id].first_in;
93      nodes[u._id].first_out = nodes[v._id].first_in = n;
94
95      return Arc(n);
96    }
97
98    void clear() {
99      arcs.clear();
100      nodes.clear();
101    }
102
103    Node source(Arc a) const { return Node(arcs[a._id].source); }
104    Node target(Arc a) const { return Node(arcs[a._id].target); }
105
106    static int id(Node v) { return v._id; }
107    static int id(Arc a) { return a._id; }
108
109    static Node nodeFromId(int id) { return Node(id);}
110    static Arc arcFromId(int id) { return Arc(id);}
111
112    bool valid(Node n) const {
113      return n._id >= 0 && n._id < static_cast<int>(nodes.size());
114    }
115    bool valid(Arc a) const {
116      return a._id >= 0 && a._id < static_cast<int>(arcs.size());
117    }
118
119    class Node {
120      friend class SmartDigraphBase;
121      friend class SmartDigraph;
122
123    protected:
124      int _id;
125      explicit Node(int id) : _id(id) {}
126    public:
127      Node() {}
128      Node (Invalid) : _id(-1) {}
129      bool operator==(const Node i) const {return _id == i._id;}
130      bool operator!=(const Node i) const {return _id != i._id;}
131      bool operator<(const Node i) const {return _id < i._id;}
132    };
133
134
135    class Arc {
136      friend class SmartDigraphBase;
137      friend class SmartDigraph;
138
139    protected:
140      int _id;
141      explicit Arc(int id) : _id(id) {}
142    public:
143      Arc() { }
144      Arc (Invalid) : _id(-1) {}
145      bool operator==(const Arc i) const {return _id == i._id;}
146      bool operator!=(const Arc i) const {return _id != i._id;}
147      bool operator<(const Arc i) const {return _id < i._id;}
148    };
149
150    void first(Node& node) const {
151      node._id = nodes.size() - 1;
152    }
153
154    static void next(Node& node) {
155      --node._id;
156    }
157
158    void first(Arc& arc) const {
159      arc._id = arcs.size() - 1;
160    }
161
162    static void next(Arc& arc) {
163      --arc._id;
164    }
165
166    void firstOut(Arc& arc, const Node& node) const {
167      arc._id = nodes[node._id].first_out;
168    }
169
170    void nextOut(Arc& arc) const {
171      arc._id = arcs[arc._id].next_out;
172    }
173
174    void firstIn(Arc& arc, const Node& node) const {
175      arc._id = nodes[node._id].first_in;
176    }
177
178    void nextIn(Arc& arc) const {
179      arc._id = arcs[arc._id].next_in;
180    }
181
182  };
183
184  typedef DigraphExtender<SmartDigraphBase> ExtendedSmartDigraphBase;
185
186  ///\ingroup graphs
187  ///
188  ///\brief A smart directed graph class.
189  ///
190  ///This is a simple and fast digraph implementation.
191  ///It is also quite memory efficient, but at the price
192  ///that <b> it does support only limited (only stack-like)
193  ///node and arc deletions</b>.
194  ///It conforms to the \ref concepts::Digraph "Digraph concept" with
195  ///an important extra feature that its maps are real \ref
196  ///concepts::ReferenceMap "reference map"s.
197  ///
198  ///\sa concepts::Digraph.
199  class SmartDigraph : public ExtendedSmartDigraphBase {
200  public:
201
202    typedef ExtendedSmartDigraphBase Parent;
203
204  private:
205
206    ///SmartDigraph is \e not copy constructible. Use DigraphCopy() instead.
207
208    ///SmartDigraph is \e not copy constructible. Use DigraphCopy() instead.
209    ///
210    SmartDigraph(const SmartDigraph &) : ExtendedSmartDigraphBase() {};
211    ///\brief Assignment of SmartDigraph to another one is \e not allowed.
212    ///Use DigraphCopy() instead.
213
214    ///Assignment of SmartDigraph to another one is \e not allowed.
215    ///Use DigraphCopy() instead.
216    void operator=(const SmartDigraph &) {}
217
218  public:
219
220    /// Constructor
221
222    /// Constructor.
223    ///
224    SmartDigraph() {};
225
226    ///Add a new node to the digraph.
227
228    /// \return the new node.
229    ///
230    Node addNode() { return Parent::addNode(); }
231
232    ///Add a new arc to the digraph.
233
234    ///Add a new arc to the digraph with source node \c s
235    ///and target node \c t.
236    ///\return the new arc.
237    Arc addArc(const Node& s, const Node& t) {
238      return Parent::addArc(s, t);
239    }
240
241    /// \brief Using this it is possible to avoid the superfluous memory
242    /// allocation.
243
244    /// Using this it is possible to avoid the superfluous memory
245    /// allocation: if you know that the digraph you want to build will
246    /// be very large (e.g. it will contain millions of nodes and/or arcs)
247    /// then it is worth reserving space for this amount before starting
248    /// to build the digraph.
249    /// \sa reserveArc
250    void reserveNode(int n) { nodes.reserve(n); };
251
252    /// \brief Using this it is possible to avoid the superfluous memory
253    /// allocation.
254
255    /// Using this it is possible to avoid the superfluous memory
256    /// allocation: if you know that the digraph you want to build will
257    /// be very large (e.g. it will contain millions of nodes and/or arcs)
258    /// then it is worth reserving space for this amount before starting
259    /// to build the digraph.
260    /// \sa reserveNode
261    void reserveArc(int m) { arcs.reserve(m); };
262
263    /// \brief Node validity check
264    ///
265    /// This function gives back true if the given node is valid,
266    /// ie. it is a real node of the graph.
267    ///
268    /// \warning A removed node (using Snapshot) could become valid again
269    /// when new nodes are added to the graph.
270    bool valid(Node n) const { return Parent::valid(n); }
271
272    /// \brief Arc validity check
273    ///
274    /// This function gives back true if the given arc is valid,
275    /// ie. it is a real arc of the graph.
276    ///
277    /// \warning A removed arc (using Snapshot) could become valid again
278    /// when new arcs are added to the graph.
279    bool valid(Arc a) const { return Parent::valid(a); }
280
281    ///Clear the digraph.
282
283    ///Erase all the nodes and arcs from the digraph.
284    ///
285    void clear() {
286      Parent::clear();
287    }
288
289    ///Split a node.
290
291    ///This function splits a node. First a new node is added to the digraph,
292    ///then the source of each outgoing arc of \c n is moved to this new node.
293    ///If \c connect is \c true (this is the default value), then a new arc
294    ///from \c n to the newly created node is also added.
295    ///\return The newly created node.
296    ///
297    ///\note The <tt>Arc</tt>s
298    ///referencing a moved arc remain
299    ///valid. However <tt>InArc</tt>'s and <tt>OutArc</tt>'s
300    ///may be invalidated.
301    ///\warning This functionality cannot be used together with the Snapshot
302    ///feature.
303    Node split(Node n, bool connect = true)
304    {
305      Node b = addNode();
306      nodes[b._id].first_out=nodes[n._id].first_out;
307      nodes[n._id].first_out=-1;
308      for(int i=nodes[b._id].first_out; i!=-1; i=arcs[i].next_out) {
309        arcs[i].source=b._id;
310      }
311      if(connect) addArc(n,b);
312      return b;
313    }
314
315  public:
316
317    class Snapshot;
318
319  protected:
320
321    void restoreSnapshot(const Snapshot &s)
322    {
323      while(s.arc_num<arcs.size()) {
324        Arc arc = arcFromId(arcs.size()-1);
325        Parent::notifier(Arc()).erase(arc);
326        nodes[arcs.back().source].first_out=arcs.back().next_out;
327        nodes[arcs.back().target].first_in=arcs.back().next_in;
328        arcs.pop_back();
329      }
330      while(s.node_num<nodes.size()) {
331        Node node = nodeFromId(nodes.size()-1);
332        Parent::notifier(Node()).erase(node);
333        nodes.pop_back();
334      }
335    }
336
337  public:
338
339    ///Class to make a snapshot of the digraph and to restrore to it later.
340
341    ///Class to make a snapshot of the digraph and to restrore to it later.
342    ///
343    ///The newly added nodes and arcs can be removed using the
344    ///restore() function.
345    ///\note After you restore a state, you cannot restore
346    ///a later state, in other word you cannot add again the arcs deleted
347    ///by restore() using another one Snapshot instance.
348    ///
349    ///\warning If you do not use correctly the snapshot that can cause
350    ///either broken program, invalid state of the digraph, valid but
351    ///not the restored digraph or no change. Because the runtime performance
352    ///the validity of the snapshot is not stored.
353    class Snapshot
354    {
355      SmartDigraph *_graph;
356    protected:
357      friend class SmartDigraph;
358      unsigned int node_num;
359      unsigned int arc_num;
360    public:
361      ///Default constructor.
362
363      ///Default constructor.
364      ///To actually make a snapshot you must call save().
365      ///
366      Snapshot() : _graph(0) {}
367      ///Constructor that immediately makes a snapshot
368
369      ///This constructor immediately makes a snapshot of the digraph.
370      ///\param graph The digraph we make a snapshot of.
371      Snapshot(SmartDigraph &graph) : _graph(&graph) {
372        node_num=_graph->nodes.size();
373        arc_num=_graph->arcs.size();
374      }
375
376      ///Make a snapshot.
377
378      ///Make a snapshot of the digraph.
379      ///
380      ///This function can be called more than once. In case of a repeated
381      ///call, the previous snapshot gets lost.
382      ///\param graph The digraph we make the snapshot of.
383      void save(SmartDigraph &graph)
384      {
385        _graph=&graph;
386        node_num=_graph->nodes.size();
387        arc_num=_graph->arcs.size();
388      }
389
390      ///Undo the changes until a snapshot.
391
392      ///Undo the changes until a snapshot created by save().
393      ///
394      ///\note After you restored a state, you cannot restore
395      ///a later state, in other word you cannot add again the arcs deleted
396      ///by restore().
397      void restore()
398      {
399        _graph->restoreSnapshot(*this);
400      }
401    };
402  };
403
404
405  class SmartGraphBase {
406
407  protected:
408
409    struct NodeT {
410      int first_out;
411    };
412
413    struct ArcT {
414      int target;
415      int next_out;
416    };
417
418    std::vector<NodeT> nodes;
419    std::vector<ArcT> arcs;
420
421    int first_free_arc;
422
423  public:
424
425    typedef SmartGraphBase Digraph;
426
427    class Node;
428    class Arc;
429    class Edge;
430
431    class Node {
432      friend class SmartGraphBase;
433    protected:
434
435      int _id;
436      explicit Node(int id) { _id = id;}
437
438    public:
439      Node() {}
440      Node (Invalid) { _id = -1; }
441      bool operator==(const Node& node) const {return _id == node._id;}
442      bool operator!=(const Node& node) const {return _id != node._id;}
443      bool operator<(const Node& node) const {return _id < node._id;}
444    };
445
446    class Edge {
447      friend class SmartGraphBase;
448    protected:
449
450      int _id;
451      explicit Edge(int id) { _id = id;}
452
453    public:
454      Edge() {}
455      Edge (Invalid) { _id = -1; }
456      bool operator==(const Edge& arc) const {return _id == arc._id;}
457      bool operator!=(const Edge& arc) const {return _id != arc._id;}
458      bool operator<(const Edge& arc) const {return _id < arc._id;}
459    };
460
461    class Arc {
462      friend class SmartGraphBase;
463    protected:
464
465      int _id;
466      explicit Arc(int id) { _id = id;}
467
468    public:
469      operator Edge() const {
470        return _id != -1 ? edgeFromId(_id / 2) : INVALID;
471      }
472
473      Arc() {}
474      Arc (Invalid) { _id = -1; }
475      bool operator==(const Arc& arc) const {return _id == arc._id;}
476      bool operator!=(const Arc& arc) const {return _id != arc._id;}
477      bool operator<(const Arc& arc) const {return _id < arc._id;}
478    };
479
480
481
482    SmartGraphBase()
483      : nodes(), arcs() {}
484
485    typedef True NodeNumTag;
486    typedef True EdgeNumTag;
487    typedef True ArcNumTag;
488
489    int nodeNum() const { return nodes.size(); }
490    int edgeNum() const { return arcs.size() / 2; }
491    int arcNum() const { return arcs.size(); }
492
493    int maxNodeId() const { return nodes.size()-1; }
494    int maxEdgeId() const { return arcs.size() / 2 - 1; }
495    int maxArcId() const { return arcs.size()-1; }
496
497    Node source(Arc e) const { return Node(arcs[e._id ^ 1].target); }
498    Node target(Arc e) const { return Node(arcs[e._id].target); }
499
500    Node u(Edge e) const { return Node(arcs[2 * e._id].target); }
501    Node v(Edge e) const { return Node(arcs[2 * e._id + 1].target); }
502
503    static bool direction(Arc e) {
504      return (e._id & 1) == 1;
505    }
506
507    static Arc direct(Edge e, bool d) {
508      return Arc(e._id * 2 + (d ? 1 : 0));
509    }
510
511    void first(Node& node) const {
512      node._id = nodes.size() - 1;
513    }
514
515    void next(Node& node) const {
516      --node._id;
517    }
518
519    void first(Arc& arc) const {
520      arc._id = arcs.size() - 1;
521    }
522
523    void next(Arc& arc) const {
524      --arc._id;
525    }
526
527    void first(Edge& arc) const {
528      arc._id = arcs.size() / 2 - 1;
529    }
530
531    void next(Edge& arc) const {
532      --arc._id;
533    }
534
535    void firstOut(Arc &arc, const Node& v) const {
536      arc._id = nodes[v._id].first_out;
537    }
538    void nextOut(Arc &arc) const {
539      arc._id = arcs[arc._id].next_out;
540    }
541
542    void firstIn(Arc &arc, const Node& v) const {
543      arc._id = ((nodes[v._id].first_out) ^ 1);
544      if (arc._id == -2) arc._id = -1;
545    }
546    void nextIn(Arc &arc) const {
547      arc._id = ((arcs[arc._id ^ 1].next_out) ^ 1);
548      if (arc._id == -2) arc._id = -1;
549    }
550
551    void firstInc(Edge &arc, bool& d, const Node& v) const {
552      int de = nodes[v._id].first_out;
553      if (de != -1) {
554        arc._id = de / 2;
555        d = ((de & 1) == 1);
556      } else {
557        arc._id = -1;
558        d = true;
559      }
560    }
561    void nextInc(Edge &arc, bool& d) const {
562      int de = (arcs[(arc._id * 2) | (d ? 1 : 0)].next_out);
563      if (de != -1) {
564        arc._id = de / 2;
565        d = ((de & 1) == 1);
566      } else {
567        arc._id = -1;
568        d = true;
569      }
570    }
571
572    static int id(Node v) { return v._id; }
573    static int id(Arc e) { return e._id; }
574    static int id(Edge e) { return e._id; }
575
576    static Node nodeFromId(int id) { return Node(id);}
577    static Arc arcFromId(int id) { return Arc(id);}
578    static Edge edgeFromId(int id) { return Edge(id);}
579
580    bool valid(Node n) const {
581      return n._id >= 0 && n._id < static_cast<int>(nodes.size());
582    }
583    bool valid(Arc a) const {
584      return a._id >= 0 && a._id < static_cast<int>(arcs.size());
585    }
586    bool valid(Edge e) const {
587      return e._id >= 0 && 2 * e._id < static_cast<int>(arcs.size());
588    }
589
590    Node addNode() {
591      int n = nodes.size();
592      nodes.push_back(NodeT());
593      nodes[n].first_out = -1;
594
595      return Node(n);
596    }
597
598    Edge addEdge(Node u, Node v) {
599      int n = arcs.size();
600      arcs.push_back(ArcT());
601      arcs.push_back(ArcT());
602
603      arcs[n].target = u._id;
604      arcs[n | 1].target = v._id;
605
606      arcs[n].next_out = nodes[v._id].first_out;
607      nodes[v._id].first_out = n;
608
609      arcs[n | 1].next_out = nodes[u._id].first_out;
610      nodes[u._id].first_out = (n | 1);
611
612      return Edge(n / 2);
613    }
614
615    void clear() {
616      arcs.clear();
617      nodes.clear();
618    }
619
620  };
621
622  typedef GraphExtender<SmartGraphBase> ExtendedSmartGraphBase;
623
624  /// \ingroup graphs
625  ///
626  /// \brief A smart undirected graph class.
627  ///
628  /// This is a simple and fast graph implementation.
629  /// It is also quite memory efficient, but at the price
630  /// that <b> it does support only limited (only stack-like)
631  /// node and arc deletions</b>.
632  /// Except from this it conforms to
633  /// the \ref concepts::Graph "Graph concept".
634  ///
635  /// It also has an
636  /// important extra feature that
637  /// its maps are real \ref concepts::ReferenceMap "reference map"s.
638  ///
639  /// \sa concepts::Graph.
640  ///
641  class SmartGraph : public ExtendedSmartGraphBase {
642  private:
643
644    ///SmartGraph is \e not copy constructible. Use GraphCopy() instead.
645
646    ///SmartGraph is \e not copy constructible. Use GraphCopy() instead.
647    ///
648    SmartGraph(const SmartGraph &) : ExtendedSmartGraphBase() {};
649
650    ///\brief Assignment of SmartGraph to another one is \e not allowed.
651    ///Use GraphCopy() instead.
652
653    ///Assignment of SmartGraph to another one is \e not allowed.
654    ///Use GraphCopy() instead.
655    void operator=(const SmartGraph &) {}
656
657  public:
658
659    typedef ExtendedSmartGraphBase Parent;
660
661    /// Constructor
662
663    /// Constructor.
664    ///
665    SmartGraph() {}
666
667    ///Add a new node to the graph.
668
669    /// \return the new node.
670    ///
671    Node addNode() { return Parent::addNode(); }
672
673    ///Add a new edge to the graph.
674
675    ///Add a new edge to the graph with node \c s
676    ///and \c t.
677    ///\return the new edge.
678    Edge addEdge(const Node& s, const Node& t) {
679      return Parent::addEdge(s, t);
680    }
681
682    /// \brief Node validity check
683    ///
684    /// This function gives back true if the given node is valid,
685    /// ie. it is a real node of the graph.
686    ///
687    /// \warning A removed node (using Snapshot) could become valid again
688    /// when new nodes are added to the graph.
689    bool valid(Node n) const { return Parent::valid(n); }
690
691    /// \brief Arc validity check
692    ///
693    /// This function gives back true if the given arc is valid,
694    /// ie. it is a real arc of the graph.
695    ///
696    /// \warning A removed arc (using Snapshot) could become valid again
697    /// when new edges are added to the graph.
698    bool valid(Arc a) const { return Parent::valid(a); }
699
700    /// \brief Edge validity check
701    ///
702    /// This function gives back true if the given edge is valid,
703    /// ie. it is a real edge of the graph.
704    ///
705    /// \warning A removed edge (using Snapshot) could become valid again
706    /// when new edges are added to the graph.
707    bool valid(Edge e) const { return Parent::valid(e); }
708
709    ///Clear the graph.
710
711    ///Erase all the nodes and edges from the graph.
712    ///
713    void clear() {
714      Parent::clear();
715    }
716
717  public:
718
719    class Snapshot;
720
721  protected:
722
723    void saveSnapshot(Snapshot &s)
724    {
725      s._graph = this;
726      s.node_num = nodes.size();
727      s.arc_num = arcs.size();
728    }
729
730    void restoreSnapshot(const Snapshot &s)
731    {
732      while(s.arc_num<arcs.size()) {
733        int n=arcs.size()-1;
734        Edge arc=edgeFromId(n/2);
735        Parent::notifier(Edge()).erase(arc);
736        std::vector<Arc> dir;
737        dir.push_back(arcFromId(n));
738        dir.push_back(arcFromId(n-1));
739        Parent::notifier(Arc()).erase(dir);
740        nodes[arcs[n-1].target].first_out=arcs[n].next_out;
741        nodes[arcs[n].target].first_out=arcs[n-1].next_out;
742        arcs.pop_back();
743        arcs.pop_back();
744      }
745      while(s.node_num<nodes.size()) {
746        int n=nodes.size()-1;
747        Node node = nodeFromId(n);
748        Parent::notifier(Node()).erase(node);
749        nodes.pop_back();
750      }
751    }
752
753  public:
754
755    ///Class to make a snapshot of the digraph and to restrore to it later.
756
757    ///Class to make a snapshot of the digraph and to restrore to it later.
758    ///
759    ///The newly added nodes and arcs can be removed using the
760    ///restore() function.
761    ///
762    ///\note After you restore a state, you cannot restore
763    ///a later state, in other word you cannot add again the arcs deleted
764    ///by restore() using another one Snapshot instance.
765    ///
766    ///\warning If you do not use correctly the snapshot that can cause
767    ///either broken program, invalid state of the digraph, valid but
768    ///not the restored digraph or no change. Because the runtime performance
769    ///the validity of the snapshot is not stored.
770    class Snapshot
771    {
772      SmartGraph *_graph;
773    protected:
774      friend class SmartGraph;
775      unsigned int node_num;
776      unsigned int arc_num;
777    public:
778      ///Default constructor.
779
780      ///Default constructor.
781      ///To actually make a snapshot you must call save().
782      ///
783      Snapshot() : _graph(0) {}
784      ///Constructor that immediately makes a snapshot
785
786      ///This constructor immediately makes a snapshot of the digraph.
787      ///\param graph The digraph we make a snapshot of.
788      Snapshot(SmartGraph &graph) {
789        graph.saveSnapshot(*this);
790      }
791
792      ///Make a snapshot.
793
794      ///Make a snapshot of the graph.
795      ///
796      ///This function can be called more than once. In case of a repeated
797      ///call, the previous snapshot gets lost.
798      ///\param graph The digraph we make the snapshot of.
799      void save(SmartGraph &graph)
800      {
801        graph.saveSnapshot(*this);
802      }
803
804      ///Undo the changes until a snapshot.
805
806      ///Undo the changes until a snapshot created by save().
807      ///
808      ///\note After you restored a state, you cannot restore
809      ///a later state, in other word you cannot add again the arcs deleted
810      ///by restore().
811      void restore()
812      {
813        _graph->restoreSnapshot(*this);
814      }
815    };
816  };
817
818} //namespace lemon
819
820
821#endif //LEMON_SMART_GRAPH_H
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