COIN-OR::LEMON - Graph Library

source: lemon-1.2/lemon/smart_graph.h @ 887:77704bf2a4ae

Last change on this file since 887:77704bf2a4ae was 877:141f9c0db4a3, checked in by Alpar Juttner <alpar@…>, 10 years ago

Unify the sources (#339)

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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) 2003-2010
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
36  class SmartDigraphBase {
37  protected:
38
39    struct NodeT
40    {
41      int first_in, first_out;
42      NodeT() {}
43    };
44    struct ArcT
45    {
46      int target, source, next_in, next_out;
47      ArcT() {}
48    };
49
50    std::vector<NodeT> nodes;
51    std::vector<ArcT> arcs;
52
53  public:
54
55    typedef SmartDigraphBase Digraph;
56
57    class Node;
58    class Arc;
59
60  public:
61
62    SmartDigraphBase() : nodes(), arcs() { }
63    SmartDigraphBase(const SmartDigraphBase &_g)
64      : nodes(_g.nodes), arcs(_g.arcs) { }
65
66    typedef True NodeNumTag;
67    typedef True ArcNumTag;
68
69    int nodeNum() const { return nodes.size(); }
70    int arcNum() const { return arcs.size(); }
71
72    int maxNodeId() const { return nodes.size()-1; }
73    int maxArcId() const { return arcs.size()-1; }
74
75    Node addNode() {
76      int n = nodes.size();
77      nodes.push_back(NodeT());
78      nodes[n].first_in = -1;
79      nodes[n].first_out = -1;
80      return Node(n);
81    }
82
83    Arc addArc(Node u, Node v) {
84      int n = arcs.size();
85      arcs.push_back(ArcT());
86      arcs[n].source = u._id;
87      arcs[n].target = v._id;
88      arcs[n].next_out = nodes[u._id].first_out;
89      arcs[n].next_in = nodes[v._id].first_in;
90      nodes[u._id].first_out = nodes[v._id].first_in = n;
91
92      return Arc(n);
93    }
94
95    void clear() {
96      arcs.clear();
97      nodes.clear();
98    }
99
100    Node source(Arc a) const { return Node(arcs[a._id].source); }
101    Node target(Arc a) const { return Node(arcs[a._id].target); }
102
103    static int id(Node v) { return v._id; }
104    static int id(Arc a) { return a._id; }
105
106    static Node nodeFromId(int id) { return Node(id);}
107    static Arc arcFromId(int id) { return Arc(id);}
108
109    bool valid(Node n) const {
110      return n._id >= 0 && n._id < static_cast<int>(nodes.size());
111    }
112    bool valid(Arc a) const {
113      return a._id >= 0 && a._id < static_cast<int>(arcs.size());
114    }
115
116    class Node {
117      friend class SmartDigraphBase;
118      friend class SmartDigraph;
119
120    protected:
121      int _id;
122      explicit Node(int id) : _id(id) {}
123    public:
124      Node() {}
125      Node (Invalid) : _id(-1) {}
126      bool operator==(const Node i) const {return _id == i._id;}
127      bool operator!=(const Node i) const {return _id != i._id;}
128      bool operator<(const Node i) const {return _id < i._id;}
129    };
130
131
132    class Arc {
133      friend class SmartDigraphBase;
134      friend class SmartDigraph;
135
136    protected:
137      int _id;
138      explicit Arc(int id) : _id(id) {}
139    public:
140      Arc() { }
141      Arc (Invalid) : _id(-1) {}
142      bool operator==(const Arc i) const {return _id == i._id;}
143      bool operator!=(const Arc i) const {return _id != i._id;}
144      bool operator<(const Arc i) const {return _id < i._id;}
145    };
146
147    void first(Node& node) const {
148      node._id = nodes.size() - 1;
149    }
150
151    static void next(Node& node) {
152      --node._id;
153    }
154
155    void first(Arc& arc) const {
156      arc._id = arcs.size() - 1;
157    }
158
159    static void next(Arc& arc) {
160      --arc._id;
161    }
162
163    void firstOut(Arc& arc, const Node& node) const {
164      arc._id = nodes[node._id].first_out;
165    }
166
167    void nextOut(Arc& arc) const {
168      arc._id = arcs[arc._id].next_out;
169    }
170
171    void firstIn(Arc& arc, const Node& node) const {
172      arc._id = nodes[node._id].first_in;
173    }
174
175    void nextIn(Arc& arc) const {
176      arc._id = arcs[arc._id].next_in;
177    }
178
179  };
180
181  typedef DigraphExtender<SmartDigraphBase> ExtendedSmartDigraphBase;
182
183  ///\ingroup graphs
184  ///
185  ///\brief A smart directed graph class.
186  ///
187  ///\ref SmartDigraph is a simple and fast digraph implementation.
188  ///It is also quite memory efficient but at the price
189  ///that it does not support node and arc deletion
190  ///(except for the Snapshot feature).
191  ///
192  ///This type fully conforms to the \ref concepts::Digraph "Digraph concept"
193  ///and it also provides some additional functionalities.
194  ///Most of its member functions and nested classes are documented
195  ///only in the concept class.
196  ///
197  ///This class provides constant time counting for nodes and arcs.
198  ///
199  ///\sa concepts::Digraph
200  ///\sa SmartGraph
201  class SmartDigraph : public ExtendedSmartDigraphBase {
202    typedef ExtendedSmartDigraphBase Parent;
203
204  private:
205    /// Digraphs are \e not copy constructible. Use DigraphCopy instead.
206    SmartDigraph(const SmartDigraph &) : ExtendedSmartDigraphBase() {};
207    /// \brief Assignment of a digraph to another one is \e not allowed.
208    /// Use DigraphCopy instead.
209    void operator=(const SmartDigraph &) {}
210
211  public:
212
213    /// Constructor
214
215    /// Constructor.
216    ///
217    SmartDigraph() {};
218
219    ///Add a new node to the digraph.
220
221    ///This function adds a new node to the digraph.
222    ///\return The new node.
223    Node addNode() { return Parent::addNode(); }
224
225    ///Add a new arc to the digraph.
226
227    ///This function adds a new arc to the digraph with source node \c s
228    ///and target node \c t.
229    ///\return The new arc.
230    Arc addArc(Node s, Node t) {
231      return Parent::addArc(s, t);
232    }
233
234    /// \brief Node validity check
235    ///
236    /// This function gives back \c true if the given node is valid,
237    /// i.e. it is a real node of the digraph.
238    ///
239    /// \warning A removed node (using Snapshot) could become valid again
240    /// if new nodes are added to the digraph.
241    bool valid(Node n) const { return Parent::valid(n); }
242
243    /// \brief Arc validity check
244    ///
245    /// This function gives back \c true if the given arc is valid,
246    /// i.e. it is a real arc of the digraph.
247    ///
248    /// \warning A removed arc (using Snapshot) could become valid again
249    /// if new arcs are added to the graph.
250    bool valid(Arc a) const { return Parent::valid(a); }
251
252    ///Split a node.
253
254    ///This function splits the given node. First, a new node is added
255    ///to the digraph, then the source of each outgoing arc of node \c n
256    ///is moved to this new node.
257    ///If the second parameter \c connect is \c true (this is the default
258    ///value), then a new arc from node \c n to the newly created node
259    ///is also added.
260    ///\return The newly created node.
261    ///
262    ///\note All iterators remain valid.
263    ///
264    ///\warning This functionality cannot be used together with the Snapshot
265    ///feature.
266    Node split(Node n, bool connect = true)
267    {
268      Node b = addNode();
269      nodes[b._id].first_out=nodes[n._id].first_out;
270      nodes[n._id].first_out=-1;
271      for(int i=nodes[b._id].first_out; i!=-1; i=arcs[i].next_out) {
272        arcs[i].source=b._id;
273      }
274      if(connect) addArc(n,b);
275      return b;
276    }
277
278    ///Clear the digraph.
279
280    ///This function erases all nodes and arcs from the digraph.
281    ///
282    void clear() {
283      Parent::clear();
284    }
285
286    /// Reserve memory for nodes.
287
288    /// Using this function, it is possible to avoid superfluous memory
289    /// allocation: if you know that the digraph you want to build will
290    /// be large (e.g. it will contain millions of nodes and/or arcs),
291    /// then it is worth reserving space for this amount before starting
292    /// to build the digraph.
293    /// \sa reserveArc()
294    void reserveNode(int n) { nodes.reserve(n); };
295
296    /// Reserve memory for arcs.
297
298    /// Using this function, it is possible to avoid superfluous memory
299    /// allocation: if you know that the digraph you want to build will
300    /// be large (e.g. it will contain millions of nodes and/or arcs),
301    /// then it is worth reserving space for this amount before starting
302    /// to build the digraph.
303    /// \sa reserveNode()
304    void reserveArc(int m) { arcs.reserve(m); };
305
306  public:
307
308    class Snapshot;
309
310  protected:
311
312    void restoreSnapshot(const Snapshot &s)
313    {
314      while(s.arc_num<arcs.size()) {
315        Arc arc = arcFromId(arcs.size()-1);
316        Parent::notifier(Arc()).erase(arc);
317        nodes[arcs.back().source].first_out=arcs.back().next_out;
318        nodes[arcs.back().target].first_in=arcs.back().next_in;
319        arcs.pop_back();
320      }
321      while(s.node_num<nodes.size()) {
322        Node node = nodeFromId(nodes.size()-1);
323        Parent::notifier(Node()).erase(node);
324        nodes.pop_back();
325      }
326    }
327
328  public:
329
330    ///Class to make a snapshot of the digraph and to restore it later.
331
332    ///Class to make a snapshot of the digraph and to restore it later.
333    ///
334    ///The newly added nodes and arcs can be removed using the
335    ///restore() function. This is the only way for deleting nodes and/or
336    ///arcs from a SmartDigraph structure.
337    ///
338    ///\note After a state is restored, you cannot restore a later state,
339    ///i.e. you cannot add the removed nodes and arcs again using
340    ///another Snapshot instance.
341    ///
342    ///\warning Node splitting cannot be restored.
343    ///\warning The validity of the snapshot is not stored due to
344    ///performance reasons. If you do not use the snapshot correctly,
345    ///it can cause broken program, invalid or not restored state of
346    ///the digraph or no change.
347    class Snapshot
348    {
349      SmartDigraph *_graph;
350    protected:
351      friend class SmartDigraph;
352      unsigned int node_num;
353      unsigned int arc_num;
354    public:
355      ///Default constructor.
356
357      ///Default constructor.
358      ///You have to call save() to actually make a snapshot.
359      Snapshot() : _graph(0) {}
360      ///Constructor that immediately makes a snapshot
361
362      ///This constructor immediately makes a snapshot of the given digraph.
363      ///
364      Snapshot(SmartDigraph &gr) : _graph(&gr) {
365        node_num=_graph->nodes.size();
366        arc_num=_graph->arcs.size();
367      }
368
369      ///Make a snapshot.
370
371      ///This function makes a snapshot of the given digraph.
372      ///It can be called more than once. In case of a repeated
373      ///call, the previous snapshot gets lost.
374      void save(SmartDigraph &gr) {
375        _graph=&gr;
376        node_num=_graph->nodes.size();
377        arc_num=_graph->arcs.size();
378      }
379
380      ///Undo the changes until a snapshot.
381
382      ///This function undos the changes until the last snapshot
383      ///created by save() or Snapshot(SmartDigraph&).
384      void restore()
385      {
386        _graph->restoreSnapshot(*this);
387      }
388    };
389  };
390
391
392  class SmartGraphBase {
393
394  protected:
395
396    struct NodeT {
397      int first_out;
398    };
399
400    struct ArcT {
401      int target;
402      int next_out;
403    };
404
405    std::vector<NodeT> nodes;
406    std::vector<ArcT> arcs;
407
408    int first_free_arc;
409
410  public:
411
412    typedef SmartGraphBase Graph;
413
414    class Node;
415    class Arc;
416    class Edge;
417
418    class Node {
419      friend class SmartGraphBase;
420    protected:
421
422      int _id;
423      explicit Node(int id) { _id = id;}
424
425    public:
426      Node() {}
427      Node (Invalid) { _id = -1; }
428      bool operator==(const Node& node) const {return _id == node._id;}
429      bool operator!=(const Node& node) const {return _id != node._id;}
430      bool operator<(const Node& node) const {return _id < node._id;}
431    };
432
433    class Edge {
434      friend class SmartGraphBase;
435    protected:
436
437      int _id;
438      explicit Edge(int id) { _id = id;}
439
440    public:
441      Edge() {}
442      Edge (Invalid) { _id = -1; }
443      bool operator==(const Edge& arc) const {return _id == arc._id;}
444      bool operator!=(const Edge& arc) const {return _id != arc._id;}
445      bool operator<(const Edge& arc) const {return _id < arc._id;}
446    };
447
448    class Arc {
449      friend class SmartGraphBase;
450    protected:
451
452      int _id;
453      explicit Arc(int id) { _id = id;}
454
455    public:
456      operator Edge() const {
457        return _id != -1 ? edgeFromId(_id / 2) : INVALID;
458      }
459
460      Arc() {}
461      Arc (Invalid) { _id = -1; }
462      bool operator==(const Arc& arc) const {return _id == arc._id;}
463      bool operator!=(const Arc& arc) const {return _id != arc._id;}
464      bool operator<(const Arc& arc) const {return _id < arc._id;}
465    };
466
467
468
469    SmartGraphBase()
470      : nodes(), arcs() {}
471
472    typedef True NodeNumTag;
473    typedef True EdgeNumTag;
474    typedef True ArcNumTag;
475
476    int nodeNum() const { return nodes.size(); }
477    int edgeNum() const { return arcs.size() / 2; }
478    int arcNum() const { return arcs.size(); }
479
480    int maxNodeId() const { return nodes.size()-1; }
481    int maxEdgeId() const { return arcs.size() / 2 - 1; }
482    int maxArcId() const { return arcs.size()-1; }
483
484    Node source(Arc e) const { return Node(arcs[e._id ^ 1].target); }
485    Node target(Arc e) const { return Node(arcs[e._id].target); }
486
487    Node u(Edge e) const { return Node(arcs[2 * e._id].target); }
488    Node v(Edge e) const { return Node(arcs[2 * e._id + 1].target); }
489
490    static bool direction(Arc e) {
491      return (e._id & 1) == 1;
492    }
493
494    static Arc direct(Edge e, bool d) {
495      return Arc(e._id * 2 + (d ? 1 : 0));
496    }
497
498    void first(Node& node) const {
499      node._id = nodes.size() - 1;
500    }
501
502    static void next(Node& node) {
503      --node._id;
504    }
505
506    void first(Arc& arc) const {
507      arc._id = arcs.size() - 1;
508    }
509
510    static void next(Arc& arc) {
511      --arc._id;
512    }
513
514    void first(Edge& arc) const {
515      arc._id = arcs.size() / 2 - 1;
516    }
517
518    static void next(Edge& arc) {
519      --arc._id;
520    }
521
522    void firstOut(Arc &arc, const Node& v) const {
523      arc._id = nodes[v._id].first_out;
524    }
525    void nextOut(Arc &arc) const {
526      arc._id = arcs[arc._id].next_out;
527    }
528
529    void firstIn(Arc &arc, const Node& v) const {
530      arc._id = ((nodes[v._id].first_out) ^ 1);
531      if (arc._id == -2) arc._id = -1;
532    }
533    void nextIn(Arc &arc) const {
534      arc._id = ((arcs[arc._id ^ 1].next_out) ^ 1);
535      if (arc._id == -2) arc._id = -1;
536    }
537
538    void firstInc(Edge &arc, bool& d, const Node& v) const {
539      int de = nodes[v._id].first_out;
540      if (de != -1) {
541        arc._id = de / 2;
542        d = ((de & 1) == 1);
543      } else {
544        arc._id = -1;
545        d = true;
546      }
547    }
548    void nextInc(Edge &arc, bool& d) const {
549      int de = (arcs[(arc._id * 2) | (d ? 1 : 0)].next_out);
550      if (de != -1) {
551        arc._id = de / 2;
552        d = ((de & 1) == 1);
553      } else {
554        arc._id = -1;
555        d = true;
556      }
557    }
558
559    static int id(Node v) { return v._id; }
560    static int id(Arc e) { return e._id; }
561    static int id(Edge e) { return e._id; }
562
563    static Node nodeFromId(int id) { return Node(id);}
564    static Arc arcFromId(int id) { return Arc(id);}
565    static Edge edgeFromId(int id) { return Edge(id);}
566
567    bool valid(Node n) const {
568      return n._id >= 0 && n._id < static_cast<int>(nodes.size());
569    }
570    bool valid(Arc a) const {
571      return a._id >= 0 && a._id < static_cast<int>(arcs.size());
572    }
573    bool valid(Edge e) const {
574      return e._id >= 0 && 2 * e._id < static_cast<int>(arcs.size());
575    }
576
577    Node addNode() {
578      int n = nodes.size();
579      nodes.push_back(NodeT());
580      nodes[n].first_out = -1;
581
582      return Node(n);
583    }
584
585    Edge addEdge(Node u, Node v) {
586      int n = arcs.size();
587      arcs.push_back(ArcT());
588      arcs.push_back(ArcT());
589
590      arcs[n].target = u._id;
591      arcs[n | 1].target = v._id;
592
593      arcs[n].next_out = nodes[v._id].first_out;
594      nodes[v._id].first_out = n;
595
596      arcs[n | 1].next_out = nodes[u._id].first_out;
597      nodes[u._id].first_out = (n | 1);
598
599      return Edge(n / 2);
600    }
601
602    void clear() {
603      arcs.clear();
604      nodes.clear();
605    }
606
607  };
608
609  typedef GraphExtender<SmartGraphBase> ExtendedSmartGraphBase;
610
611  /// \ingroup graphs
612  ///
613  /// \brief A smart undirected graph class.
614  ///
615  /// \ref SmartGraph is a simple and fast graph implementation.
616  /// It is also quite memory efficient but at the price
617  /// that it does not support node and edge deletion
618  /// (except for the Snapshot feature).
619  ///
620  /// This type fully conforms to the \ref concepts::Graph "Graph concept"
621  /// and it also provides some additional functionalities.
622  /// Most of its member functions and nested classes are documented
623  /// only in the concept class.
624  ///
625  /// This class provides constant time counting for nodes, edges and arcs.
626  ///
627  /// \sa concepts::Graph
628  /// \sa SmartDigraph
629  class SmartGraph : public ExtendedSmartGraphBase {
630    typedef ExtendedSmartGraphBase Parent;
631
632  private:
633    /// Graphs are \e not copy constructible. Use GraphCopy instead.
634    SmartGraph(const SmartGraph &) : ExtendedSmartGraphBase() {};
635    /// \brief Assignment of a graph to another one is \e not allowed.
636    /// Use GraphCopy instead.
637    void operator=(const SmartGraph &) {}
638
639  public:
640
641    /// Constructor
642
643    /// Constructor.
644    ///
645    SmartGraph() {}
646
647    /// \brief Add a new node to the graph.
648    ///
649    /// This function adds a new node to the graph.
650    /// \return The new node.
651    Node addNode() { return Parent::addNode(); }
652
653    /// \brief Add a new edge to the graph.
654    ///
655    /// This function adds a new edge to the graph between nodes
656    /// \c u and \c v with inherent orientation from node \c u to
657    /// node \c v.
658    /// \return The new edge.
659    Edge addEdge(Node u, Node v) {
660      return Parent::addEdge(u, v);
661    }
662
663    /// \brief Node validity check
664    ///
665    /// This function gives back \c true if the given node is valid,
666    /// i.e. it is a real node of the graph.
667    ///
668    /// \warning A removed node (using Snapshot) could become valid again
669    /// if new nodes are added to the graph.
670    bool valid(Node n) const { return Parent::valid(n); }
671
672    /// \brief Edge validity check
673    ///
674    /// This function gives back \c true if the given edge is valid,
675    /// i.e. it is a real edge of the graph.
676    ///
677    /// \warning A removed edge (using Snapshot) could become valid again
678    /// if new edges are added to the graph.
679    bool valid(Edge e) const { return Parent::valid(e); }
680
681    /// \brief Arc validity check
682    ///
683    /// This function gives back \c true if the given arc is valid,
684    /// i.e. it is a real arc of the graph.
685    ///
686    /// \warning A removed arc (using Snapshot) could become valid again
687    /// if new edges are added to the graph.
688    bool valid(Arc a) const { return Parent::valid(a); }
689
690    ///Clear the graph.
691
692    ///This function erases all nodes and arcs from the graph.
693    ///
694    void clear() {
695      Parent::clear();
696    }
697
698    /// Reserve memory for nodes.
699
700    /// Using this function, it is possible to avoid superfluous memory
701    /// allocation: if you know that the graph you want to build will
702    /// be large (e.g. it will contain millions of nodes and/or edges),
703    /// then it is worth reserving space for this amount before starting
704    /// to build the graph.
705    /// \sa reserveEdge()
706    void reserveNode(int n) { nodes.reserve(n); };
707
708    /// Reserve memory for edges.
709
710    /// Using this function, it is possible to avoid superfluous memory
711    /// allocation: if you know that the graph you want to build will
712    /// be large (e.g. it will contain millions of nodes and/or edges),
713    /// then it is worth reserving space for this amount before starting
714    /// to build the graph.
715    /// \sa reserveNode()
716    void reserveEdge(int m) { arcs.reserve(2 * m); };
717
718  public:
719
720    class Snapshot;
721
722  protected:
723
724    void saveSnapshot(Snapshot &s)
725    {
726      s._graph = this;
727      s.node_num = nodes.size();
728      s.arc_num = arcs.size();
729    }
730
731    void restoreSnapshot(const Snapshot &s)
732    {
733      while(s.arc_num<arcs.size()) {
734        int n=arcs.size()-1;
735        Edge arc=edgeFromId(n/2);
736        Parent::notifier(Edge()).erase(arc);
737        std::vector<Arc> dir;
738        dir.push_back(arcFromId(n));
739        dir.push_back(arcFromId(n-1));
740        Parent::notifier(Arc()).erase(dir);
741        nodes[arcs[n-1].target].first_out=arcs[n].next_out;
742        nodes[arcs[n].target].first_out=arcs[n-1].next_out;
743        arcs.pop_back();
744        arcs.pop_back();
745      }
746      while(s.node_num<nodes.size()) {
747        int n=nodes.size()-1;
748        Node node = nodeFromId(n);
749        Parent::notifier(Node()).erase(node);
750        nodes.pop_back();
751      }
752    }
753
754  public:
755
756    ///Class to make a snapshot of the graph and to restore it later.
757
758    ///Class to make a snapshot of the graph and to restore it later.
759    ///
760    ///The newly added nodes and edges can be removed using the
761    ///restore() function. This is the only way for deleting nodes and/or
762    ///edges from a SmartGraph structure.
763    ///
764    ///\note After a state is restored, you cannot restore a later state,
765    ///i.e. you cannot add the removed nodes and edges again using
766    ///another Snapshot instance.
767    ///
768    ///\warning The validity of the snapshot is not stored due to
769    ///performance reasons. If you do not use the snapshot correctly,
770    ///it can cause broken program, invalid or not restored state of
771    ///the graph or no change.
772    class Snapshot
773    {
774      SmartGraph *_graph;
775    protected:
776      friend class SmartGraph;
777      unsigned int node_num;
778      unsigned int arc_num;
779    public:
780      ///Default constructor.
781
782      ///Default constructor.
783      ///You have to call save() to actually make a snapshot.
784      Snapshot() : _graph(0) {}
785      ///Constructor that immediately makes a snapshot
786
787      /// This constructor immediately makes a snapshot of the given graph.
788      ///
789      Snapshot(SmartGraph &gr) {
790        gr.saveSnapshot(*this);
791      }
792
793      ///Make a snapshot.
794
795      ///This function makes a snapshot of the given graph.
796      ///It can be called more than once. In case of a repeated
797      ///call, the previous snapshot gets lost.
798      void save(SmartGraph &gr)
799      {
800        gr.saveSnapshot(*this);
801      }
802
803      ///Undo the changes until the last snapshot.
804
805      ///This function undos the changes until the last snapshot
806      ///created by save() or Snapshot(SmartGraph&).
807      void restore()
808      {
809        _graph->restoreSnapshot(*this);
810      }
811    };
812  };
813
814} //namespace lemon
815
816
817#endif //LEMON_SMART_GRAPH_H
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