lemon/list_graph.h
author Alpar Juttner <alpar@cs.elte.hu>
Fri, 12 Dec 2008 21:52:53 +0000
branch1.0
changeset 350 d5cfcff85dfd
parent 280 e7f8647ce760
child 427 c59bdcc8e33e
permissions -rw-r--r--
Merge bugfix #195
     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_LIST_GRAPH_H
    20 #define LEMON_LIST_GRAPH_H
    21 
    22 ///\ingroup graphs
    23 ///\file
    24 ///\brief ListDigraph, ListGraph classes.
    25 
    26 #include <lemon/core.h>
    27 #include <lemon/error.h>
    28 #include <lemon/bits/graph_extender.h>
    29 
    30 #include <vector>
    31 #include <list>
    32 
    33 namespace lemon {
    34 
    35   class ListDigraphBase {
    36 
    37   protected:
    38     struct NodeT {
    39       int first_in, first_out;
    40       int prev, next;
    41     };
    42 
    43     struct ArcT {
    44       int target, source;
    45       int prev_in, prev_out;
    46       int next_in, next_out;
    47     };
    48 
    49     std::vector<NodeT> nodes;
    50 
    51     int first_node;
    52 
    53     int first_free_node;
    54 
    55     std::vector<ArcT> arcs;
    56 
    57     int first_free_arc;
    58 
    59   public:
    60 
    61     typedef ListDigraphBase Digraph;
    62 
    63     class Node {
    64       friend class ListDigraphBase;
    65     protected:
    66 
    67       int id;
    68       explicit Node(int pid) { id = pid;}
    69 
    70     public:
    71       Node() {}
    72       Node (Invalid) { id = -1; }
    73       bool operator==(const Node& node) const {return id == node.id;}
    74       bool operator!=(const Node& node) const {return id != node.id;}
    75       bool operator<(const Node& node) const {return id < node.id;}
    76     };
    77 
    78     class Arc {
    79       friend class ListDigraphBase;
    80     protected:
    81 
    82       int id;
    83       explicit Arc(int pid) { id = pid;}
    84 
    85     public:
    86       Arc() {}
    87       Arc (Invalid) { id = -1; }
    88       bool operator==(const Arc& arc) const {return id == arc.id;}
    89       bool operator!=(const Arc& arc) const {return id != arc.id;}
    90       bool operator<(const Arc& arc) const {return id < arc.id;}
    91     };
    92 
    93 
    94 
    95     ListDigraphBase()
    96       : nodes(), first_node(-1),
    97         first_free_node(-1), arcs(), first_free_arc(-1) {}
    98 
    99 
   100     int maxNodeId() const { return nodes.size()-1; }
   101     int maxArcId() const { return arcs.size()-1; }
   102 
   103     Node source(Arc e) const { return Node(arcs[e.id].source); }
   104     Node target(Arc e) const { return Node(arcs[e.id].target); }
   105 
   106 
   107     void first(Node& node) const {
   108       node.id = first_node;
   109     }
   110 
   111     void next(Node& node) const {
   112       node.id = nodes[node.id].next;
   113     }
   114 
   115 
   116     void first(Arc& arc) const {
   117       int n;
   118       for(n = first_node;
   119           n!=-1 && nodes[n].first_in == -1;
   120           n = nodes[n].next) {}
   121       arc.id = (n == -1) ? -1 : nodes[n].first_in;
   122     }
   123 
   124     void next(Arc& arc) const {
   125       if (arcs[arc.id].next_in != -1) {
   126         arc.id = arcs[arc.id].next_in;
   127       } else {
   128         int n;
   129         for(n = nodes[arcs[arc.id].target].next;
   130             n!=-1 && nodes[n].first_in == -1;
   131             n = nodes[n].next) {}
   132         arc.id = (n == -1) ? -1 : nodes[n].first_in;
   133       }
   134     }
   135 
   136     void firstOut(Arc &e, const Node& v) const {
   137       e.id = nodes[v.id].first_out;
   138     }
   139     void nextOut(Arc &e) const {
   140       e.id=arcs[e.id].next_out;
   141     }
   142 
   143     void firstIn(Arc &e, const Node& v) const {
   144       e.id = nodes[v.id].first_in;
   145     }
   146     void nextIn(Arc &e) const {
   147       e.id=arcs[e.id].next_in;
   148     }
   149 
   150 
   151     static int id(Node v) { return v.id; }
   152     static int id(Arc e) { return e.id; }
   153 
   154     static Node nodeFromId(int id) { return Node(id);}
   155     static Arc arcFromId(int id) { return Arc(id);}
   156 
   157     bool valid(Node n) const {
   158       return n.id >= 0 && n.id < static_cast<int>(nodes.size()) &&
   159         nodes[n.id].prev != -2;
   160     }
   161 
   162     bool valid(Arc a) const {
   163       return a.id >= 0 && a.id < static_cast<int>(arcs.size()) &&
   164         arcs[a.id].prev_in != -2;
   165     }
   166 
   167     Node addNode() {
   168       int n;
   169 
   170       if(first_free_node==-1) {
   171         n = nodes.size();
   172         nodes.push_back(NodeT());
   173       } else {
   174         n = first_free_node;
   175         first_free_node = nodes[n].next;
   176       }
   177 
   178       nodes[n].next = first_node;
   179       if(first_node != -1) nodes[first_node].prev = n;
   180       first_node = n;
   181       nodes[n].prev = -1;
   182 
   183       nodes[n].first_in = nodes[n].first_out = -1;
   184 
   185       return Node(n);
   186     }
   187 
   188     Arc addArc(Node u, Node v) {
   189       int n;
   190 
   191       if (first_free_arc == -1) {
   192         n = arcs.size();
   193         arcs.push_back(ArcT());
   194       } else {
   195         n = first_free_arc;
   196         first_free_arc = arcs[n].next_in;
   197       }
   198 
   199       arcs[n].source = u.id;
   200       arcs[n].target = v.id;
   201 
   202       arcs[n].next_out = nodes[u.id].first_out;
   203       if(nodes[u.id].first_out != -1) {
   204         arcs[nodes[u.id].first_out].prev_out = n;
   205       }
   206 
   207       arcs[n].next_in = nodes[v.id].first_in;
   208       if(nodes[v.id].first_in != -1) {
   209         arcs[nodes[v.id].first_in].prev_in = n;
   210       }
   211 
   212       arcs[n].prev_in = arcs[n].prev_out = -1;
   213 
   214       nodes[u.id].first_out = nodes[v.id].first_in = n;
   215 
   216       return Arc(n);
   217     }
   218 
   219     void erase(const Node& node) {
   220       int n = node.id;
   221 
   222       if(nodes[n].next != -1) {
   223         nodes[nodes[n].next].prev = nodes[n].prev;
   224       }
   225 
   226       if(nodes[n].prev != -1) {
   227         nodes[nodes[n].prev].next = nodes[n].next;
   228       } else {
   229         first_node = nodes[n].next;
   230       }
   231 
   232       nodes[n].next = first_free_node;
   233       first_free_node = n;
   234       nodes[n].prev = -2;
   235 
   236     }
   237 
   238     void erase(const Arc& arc) {
   239       int n = arc.id;
   240 
   241       if(arcs[n].next_in!=-1) {
   242         arcs[arcs[n].next_in].prev_in = arcs[n].prev_in;
   243       }
   244 
   245       if(arcs[n].prev_in!=-1) {
   246         arcs[arcs[n].prev_in].next_in = arcs[n].next_in;
   247       } else {
   248         nodes[arcs[n].target].first_in = arcs[n].next_in;
   249       }
   250 
   251 
   252       if(arcs[n].next_out!=-1) {
   253         arcs[arcs[n].next_out].prev_out = arcs[n].prev_out;
   254       }
   255 
   256       if(arcs[n].prev_out!=-1) {
   257         arcs[arcs[n].prev_out].next_out = arcs[n].next_out;
   258       } else {
   259         nodes[arcs[n].source].first_out = arcs[n].next_out;
   260       }
   261 
   262       arcs[n].next_in = first_free_arc;
   263       first_free_arc = n;
   264       arcs[n].prev_in = -2;
   265     }
   266 
   267     void clear() {
   268       arcs.clear();
   269       nodes.clear();
   270       first_node = first_free_node = first_free_arc = -1;
   271     }
   272 
   273   protected:
   274     void changeTarget(Arc e, Node n)
   275     {
   276       if(arcs[e.id].next_in != -1)
   277         arcs[arcs[e.id].next_in].prev_in = arcs[e.id].prev_in;
   278       if(arcs[e.id].prev_in != -1)
   279         arcs[arcs[e.id].prev_in].next_in = arcs[e.id].next_in;
   280       else nodes[arcs[e.id].target].first_in = arcs[e.id].next_in;
   281       if (nodes[n.id].first_in != -1) {
   282         arcs[nodes[n.id].first_in].prev_in = e.id;
   283       }
   284       arcs[e.id].target = n.id;
   285       arcs[e.id].prev_in = -1;
   286       arcs[e.id].next_in = nodes[n.id].first_in;
   287       nodes[n.id].first_in = e.id;
   288     }
   289     void changeSource(Arc e, Node n)
   290     {
   291       if(arcs[e.id].next_out != -1)
   292         arcs[arcs[e.id].next_out].prev_out = arcs[e.id].prev_out;
   293       if(arcs[e.id].prev_out != -1)
   294         arcs[arcs[e.id].prev_out].next_out = arcs[e.id].next_out;
   295       else nodes[arcs[e.id].source].first_out = arcs[e.id].next_out;
   296       if (nodes[n.id].first_out != -1) {
   297         arcs[nodes[n.id].first_out].prev_out = e.id;
   298       }
   299       arcs[e.id].source = n.id;
   300       arcs[e.id].prev_out = -1;
   301       arcs[e.id].next_out = nodes[n.id].first_out;
   302       nodes[n.id].first_out = e.id;
   303     }
   304 
   305   };
   306 
   307   typedef DigraphExtender<ListDigraphBase> ExtendedListDigraphBase;
   308 
   309   /// \addtogroup graphs
   310   /// @{
   311 
   312   ///A general directed graph structure.
   313 
   314   ///\ref ListDigraph is a simple and fast <em>directed graph</em>
   315   ///implementation based on static linked lists that are stored in
   316   ///\c std::vector structures.
   317   ///
   318   ///It conforms to the \ref concepts::Digraph "Digraph concept" and it
   319   ///also provides several useful additional functionalities.
   320   ///Most of the member functions and nested classes are documented
   321   ///only in the concept class.
   322   ///
   323   ///An important extra feature of this digraph implementation is that
   324   ///its maps are real \ref concepts::ReferenceMap "reference map"s.
   325   ///
   326   ///\sa concepts::Digraph
   327 
   328   class ListDigraph : public ExtendedListDigraphBase {
   329   private:
   330     ///ListDigraph is \e not copy constructible. Use copyDigraph() instead.
   331 
   332     ///ListDigraph is \e not copy constructible. Use copyDigraph() instead.
   333     ///
   334     ListDigraph(const ListDigraph &) :ExtendedListDigraphBase() {};
   335     ///\brief Assignment of ListDigraph to another one is \e not allowed.
   336     ///Use copyDigraph() instead.
   337 
   338     ///Assignment of ListDigraph to another one is \e not allowed.
   339     ///Use copyDigraph() instead.
   340     void operator=(const ListDigraph &) {}
   341   public:
   342 
   343     typedef ExtendedListDigraphBase Parent;
   344 
   345     /// Constructor
   346 
   347     /// Constructor.
   348     ///
   349     ListDigraph() {}
   350 
   351     ///Add a new node to the digraph.
   352 
   353     ///Add a new node to the digraph.
   354     ///\return the new node.
   355     Node addNode() { return Parent::addNode(); }
   356 
   357     ///Add a new arc to the digraph.
   358 
   359     ///Add a new arc to the digraph with source node \c s
   360     ///and target node \c t.
   361     ///\return the new arc.
   362     Arc addArc(const Node& s, const Node& t) {
   363       return Parent::addArc(s, t);
   364     }
   365 
   366     ///\brief Erase a node from the digraph.
   367     ///
   368     ///Erase a node from the digraph.
   369     ///
   370     void erase(const Node& n) { Parent::erase(n); }
   371 
   372     ///\brief Erase an arc from the digraph.
   373     ///
   374     ///Erase an arc from the digraph.
   375     ///
   376     void erase(const Arc& a) { Parent::erase(a); }
   377 
   378     /// Node validity check
   379 
   380     /// This function gives back true if the given node is valid,
   381     /// ie. it is a real node of the graph.
   382     ///
   383     /// \warning A Node pointing to a removed item
   384     /// could become valid again later if new nodes are
   385     /// added to the graph.
   386     bool valid(Node n) const { return Parent::valid(n); }
   387 
   388     /// Arc validity check
   389 
   390     /// This function gives back true if the given arc is valid,
   391     /// ie. it is a real arc of the graph.
   392     ///
   393     /// \warning An Arc pointing to a removed item
   394     /// could become valid again later if new nodes are
   395     /// added to the graph.
   396     bool valid(Arc a) const { return Parent::valid(a); }
   397 
   398     /// Change the target of \c a to \c n
   399 
   400     /// Change the target of \c a to \c n
   401     ///
   402     ///\note The <tt>ArcIt</tt>s and <tt>OutArcIt</tt>s referencing
   403     ///the changed arc remain valid. However <tt>InArcIt</tt>s are
   404     ///invalidated.
   405     ///
   406     ///\warning This functionality cannot be used together with the Snapshot
   407     ///feature.
   408     void changeTarget(Arc a, Node n) {
   409       Parent::changeTarget(a,n);
   410     }
   411     /// Change the source of \c a to \c n
   412 
   413     /// Change the source of \c a to \c n
   414     ///
   415     ///\note The <tt>InArcIt</tt>s referencing the changed arc remain
   416     ///valid. However the <tt>ArcIt</tt>s and <tt>OutArcIt</tt>s are
   417     ///invalidated.
   418     ///
   419     ///\warning This functionality cannot be used together with the Snapshot
   420     ///feature.
   421     void changeSource(Arc a, Node n) {
   422       Parent::changeSource(a,n);
   423     }
   424 
   425     /// Invert the direction of an arc.
   426 
   427     ///\note The <tt>ArcIt</tt>s referencing the changed arc remain
   428     ///valid. However <tt>OutArcIt</tt>s and <tt>InArcIt</tt>s are
   429     ///invalidated.
   430     ///
   431     ///\warning This functionality cannot be used together with the Snapshot
   432     ///feature.
   433     void reverseArc(Arc e) {
   434       Node t=target(e);
   435       changeTarget(e,source(e));
   436       changeSource(e,t);
   437     }
   438 
   439     /// Reserve memory for nodes.
   440 
   441     /// Using this function it is possible to avoid the superfluous memory
   442     /// allocation: if you know that the digraph you want to build will
   443     /// be very large (e.g. it will contain millions of nodes and/or arcs)
   444     /// then it is worth reserving space for this amount before starting
   445     /// to build the digraph.
   446     /// \sa reserveArc
   447     void reserveNode(int n) { nodes.reserve(n); };
   448 
   449     /// Reserve memory for arcs.
   450 
   451     /// Using this function it is possible to avoid the superfluous memory
   452     /// allocation: if you know that the digraph you want to build will
   453     /// be very large (e.g. it will contain millions of nodes and/or arcs)
   454     /// then it is worth reserving space for this amount before starting
   455     /// to build the digraph.
   456     /// \sa reserveNode
   457     void reserveArc(int m) { arcs.reserve(m); };
   458 
   459     ///Contract two nodes.
   460 
   461     ///This function contracts two nodes.
   462     ///Node \p b will be removed but instead of deleting
   463     ///incident arcs, they will be joined to \p a.
   464     ///The last parameter \p r controls whether to remove loops. \c true
   465     ///means that loops will be removed.
   466     ///
   467     ///\note The <tt>ArcIt</tt>s referencing a moved arc remain
   468     ///valid. However <tt>InArcIt</tt>s and <tt>OutArcIt</tt>s
   469     ///may be invalidated.
   470     ///
   471     ///\warning This functionality cannot be used together with the Snapshot
   472     ///feature.
   473     void contract(Node a, Node b, bool r = true)
   474     {
   475       for(OutArcIt e(*this,b);e!=INVALID;) {
   476         OutArcIt f=e;
   477         ++f;
   478         if(r && target(e)==a) erase(e);
   479         else changeSource(e,a);
   480         e=f;
   481       }
   482       for(InArcIt e(*this,b);e!=INVALID;) {
   483         InArcIt f=e;
   484         ++f;
   485         if(r && source(e)==a) erase(e);
   486         else changeTarget(e,a);
   487         e=f;
   488       }
   489       erase(b);
   490     }
   491 
   492     ///Split a node.
   493 
   494     ///This function splits a node. First a new node is added to the digraph,
   495     ///then the source of each outgoing arc of \c n is moved to this new node.
   496     ///If \c connect is \c true (this is the default value), then a new arc
   497     ///from \c n to the newly created node is also added.
   498     ///\return The newly created node.
   499     ///
   500     ///\note The <tt>ArcIt</tt>s referencing a moved arc remain
   501     ///valid. However <tt>InArcIt</tt>s and <tt>OutArcIt</tt>s may
   502     ///be invalidated.
   503     ///
   504     ///\warning This functionality cannot be used in conjunction with the
   505     ///Snapshot feature.
   506     Node split(Node n, bool connect = true) {
   507       Node b = addNode();
   508       for(OutArcIt e(*this,n);e!=INVALID;) {
   509         OutArcIt f=e;
   510         ++f;
   511         changeSource(e,b);
   512         e=f;
   513       }
   514       if (connect) addArc(n,b);
   515       return b;
   516     }
   517 
   518     ///Split an arc.
   519 
   520     ///This function splits an arc. First a new node \c b is added to
   521     ///the digraph, then the original arc is re-targeted to \c
   522     ///b. Finally an arc from \c b to the original target is added.
   523     ///
   524     ///\return The newly created node.
   525     ///
   526     ///\warning This functionality cannot be used together with the
   527     ///Snapshot feature.
   528     Node split(Arc e) {
   529       Node b = addNode();
   530       addArc(b,target(e));
   531       changeTarget(e,b);
   532       return b;
   533     }
   534 
   535     /// \brief Class to make a snapshot of the digraph and restore
   536     /// it later.
   537     ///
   538     /// Class to make a snapshot of the digraph and restore it later.
   539     ///
   540     /// The newly added nodes and arcs can be removed using the
   541     /// restore() function.
   542     ///
   543     /// \warning Arc and node deletions and other modifications (e.g.
   544     /// contracting, splitting, reversing arcs or nodes) cannot be
   545     /// restored. These events invalidate the snapshot.
   546     class Snapshot {
   547     protected:
   548 
   549       typedef Parent::NodeNotifier NodeNotifier;
   550 
   551       class NodeObserverProxy : public NodeNotifier::ObserverBase {
   552       public:
   553 
   554         NodeObserverProxy(Snapshot& _snapshot)
   555           : snapshot(_snapshot) {}
   556 
   557         using NodeNotifier::ObserverBase::attach;
   558         using NodeNotifier::ObserverBase::detach;
   559         using NodeNotifier::ObserverBase::attached;
   560 
   561       protected:
   562 
   563         virtual void add(const Node& node) {
   564           snapshot.addNode(node);
   565         }
   566         virtual void add(const std::vector<Node>& nodes) {
   567           for (int i = nodes.size() - 1; i >= 0; ++i) {
   568             snapshot.addNode(nodes[i]);
   569           }
   570         }
   571         virtual void erase(const Node& node) {
   572           snapshot.eraseNode(node);
   573         }
   574         virtual void erase(const std::vector<Node>& nodes) {
   575           for (int i = 0; i < int(nodes.size()); ++i) {
   576             snapshot.eraseNode(nodes[i]);
   577           }
   578         }
   579         virtual void build() {
   580           Node node;
   581           std::vector<Node> nodes;
   582           for (notifier()->first(node); node != INVALID;
   583                notifier()->next(node)) {
   584             nodes.push_back(node);
   585           }
   586           for (int i = nodes.size() - 1; i >= 0; --i) {
   587             snapshot.addNode(nodes[i]);
   588           }
   589         }
   590         virtual void clear() {
   591           Node node;
   592           for (notifier()->first(node); node != INVALID;
   593                notifier()->next(node)) {
   594             snapshot.eraseNode(node);
   595           }
   596         }
   597 
   598         Snapshot& snapshot;
   599       };
   600 
   601       class ArcObserverProxy : public ArcNotifier::ObserverBase {
   602       public:
   603 
   604         ArcObserverProxy(Snapshot& _snapshot)
   605           : snapshot(_snapshot) {}
   606 
   607         using ArcNotifier::ObserverBase::attach;
   608         using ArcNotifier::ObserverBase::detach;
   609         using ArcNotifier::ObserverBase::attached;
   610 
   611       protected:
   612 
   613         virtual void add(const Arc& arc) {
   614           snapshot.addArc(arc);
   615         }
   616         virtual void add(const std::vector<Arc>& arcs) {
   617           for (int i = arcs.size() - 1; i >= 0; ++i) {
   618             snapshot.addArc(arcs[i]);
   619           }
   620         }
   621         virtual void erase(const Arc& arc) {
   622           snapshot.eraseArc(arc);
   623         }
   624         virtual void erase(const std::vector<Arc>& arcs) {
   625           for (int i = 0; i < int(arcs.size()); ++i) {
   626             snapshot.eraseArc(arcs[i]);
   627           }
   628         }
   629         virtual void build() {
   630           Arc arc;
   631           std::vector<Arc> arcs;
   632           for (notifier()->first(arc); arc != INVALID;
   633                notifier()->next(arc)) {
   634             arcs.push_back(arc);
   635           }
   636           for (int i = arcs.size() - 1; i >= 0; --i) {
   637             snapshot.addArc(arcs[i]);
   638           }
   639         }
   640         virtual void clear() {
   641           Arc arc;
   642           for (notifier()->first(arc); arc != INVALID;
   643                notifier()->next(arc)) {
   644             snapshot.eraseArc(arc);
   645           }
   646         }
   647 
   648         Snapshot& snapshot;
   649       };
   650 
   651       ListDigraph *digraph;
   652 
   653       NodeObserverProxy node_observer_proxy;
   654       ArcObserverProxy arc_observer_proxy;
   655 
   656       std::list<Node> added_nodes;
   657       std::list<Arc> added_arcs;
   658 
   659 
   660       void addNode(const Node& node) {
   661         added_nodes.push_front(node);
   662       }
   663       void eraseNode(const Node& node) {
   664         std::list<Node>::iterator it =
   665           std::find(added_nodes.begin(), added_nodes.end(), node);
   666         if (it == added_nodes.end()) {
   667           clear();
   668           arc_observer_proxy.detach();
   669           throw NodeNotifier::ImmediateDetach();
   670         } else {
   671           added_nodes.erase(it);
   672         }
   673       }
   674 
   675       void addArc(const Arc& arc) {
   676         added_arcs.push_front(arc);
   677       }
   678       void eraseArc(const Arc& arc) {
   679         std::list<Arc>::iterator it =
   680           std::find(added_arcs.begin(), added_arcs.end(), arc);
   681         if (it == added_arcs.end()) {
   682           clear();
   683           node_observer_proxy.detach();
   684           throw ArcNotifier::ImmediateDetach();
   685         } else {
   686           added_arcs.erase(it);
   687         }
   688       }
   689 
   690       void attach(ListDigraph &_digraph) {
   691         digraph = &_digraph;
   692         node_observer_proxy.attach(digraph->notifier(Node()));
   693         arc_observer_proxy.attach(digraph->notifier(Arc()));
   694       }
   695 
   696       void detach() {
   697         node_observer_proxy.detach();
   698         arc_observer_proxy.detach();
   699       }
   700 
   701       bool attached() const {
   702         return node_observer_proxy.attached();
   703       }
   704 
   705       void clear() {
   706         added_nodes.clear();
   707         added_arcs.clear();
   708       }
   709 
   710     public:
   711 
   712       /// \brief Default constructor.
   713       ///
   714       /// Default constructor.
   715       /// To actually make a snapshot you must call save().
   716       Snapshot()
   717         : digraph(0), node_observer_proxy(*this),
   718           arc_observer_proxy(*this) {}
   719 
   720       /// \brief Constructor that immediately makes a snapshot.
   721       ///
   722       /// This constructor immediately makes a snapshot of the digraph.
   723       /// \param _digraph The digraph we make a snapshot of.
   724       Snapshot(ListDigraph &_digraph)
   725         : node_observer_proxy(*this),
   726           arc_observer_proxy(*this) {
   727         attach(_digraph);
   728       }
   729 
   730       /// \brief Make a snapshot.
   731       ///
   732       /// Make a snapshot of the digraph.
   733       ///
   734       /// This function can be called more than once. In case of a repeated
   735       /// call, the previous snapshot gets lost.
   736       /// \param _digraph The digraph we make the snapshot of.
   737       void save(ListDigraph &_digraph) {
   738         if (attached()) {
   739           detach();
   740           clear();
   741         }
   742         attach(_digraph);
   743       }
   744 
   745       /// \brief Undo the changes until the last snapshot.
   746       //
   747       /// Undo the changes until the last snapshot created by save().
   748       void restore() {
   749         detach();
   750         for(std::list<Arc>::iterator it = added_arcs.begin();
   751             it != added_arcs.end(); ++it) {
   752           digraph->erase(*it);
   753         }
   754         for(std::list<Node>::iterator it = added_nodes.begin();
   755             it != added_nodes.end(); ++it) {
   756           digraph->erase(*it);
   757         }
   758         clear();
   759       }
   760 
   761       /// \brief Gives back true when the snapshot is valid.
   762       ///
   763       /// Gives back true when the snapshot is valid.
   764       bool valid() const {
   765         return attached();
   766       }
   767     };
   768 
   769   };
   770 
   771   ///@}
   772 
   773   class ListGraphBase {
   774 
   775   protected:
   776 
   777     struct NodeT {
   778       int first_out;
   779       int prev, next;
   780     };
   781 
   782     struct ArcT {
   783       int target;
   784       int prev_out, next_out;
   785     };
   786 
   787     std::vector<NodeT> nodes;
   788 
   789     int first_node;
   790 
   791     int first_free_node;
   792 
   793     std::vector<ArcT> arcs;
   794 
   795     int first_free_arc;
   796 
   797   public:
   798 
   799     typedef ListGraphBase Digraph;
   800 
   801     class Node;
   802     class Arc;
   803     class Edge;
   804 
   805     class Node {
   806       friend class ListGraphBase;
   807     protected:
   808 
   809       int id;
   810       explicit Node(int pid) { id = pid;}
   811 
   812     public:
   813       Node() {}
   814       Node (Invalid) { id = -1; }
   815       bool operator==(const Node& node) const {return id == node.id;}
   816       bool operator!=(const Node& node) const {return id != node.id;}
   817       bool operator<(const Node& node) const {return id < node.id;}
   818     };
   819 
   820     class Edge {
   821       friend class ListGraphBase;
   822     protected:
   823 
   824       int id;
   825       explicit Edge(int pid) { id = pid;}
   826 
   827     public:
   828       Edge() {}
   829       Edge (Invalid) { id = -1; }
   830       bool operator==(const Edge& edge) const {return id == edge.id;}
   831       bool operator!=(const Edge& edge) const {return id != edge.id;}
   832       bool operator<(const Edge& edge) const {return id < edge.id;}
   833     };
   834 
   835     class Arc {
   836       friend class ListGraphBase;
   837     protected:
   838 
   839       int id;
   840       explicit Arc(int pid) { id = pid;}
   841 
   842     public:
   843       operator Edge() const { 
   844         return id != -1 ? edgeFromId(id / 2) : INVALID; 
   845       }
   846 
   847       Arc() {}
   848       Arc (Invalid) { id = -1; }
   849       bool operator==(const Arc& arc) const {return id == arc.id;}
   850       bool operator!=(const Arc& arc) const {return id != arc.id;}
   851       bool operator<(const Arc& arc) const {return id < arc.id;}
   852     };
   853 
   854 
   855 
   856     ListGraphBase()
   857       : nodes(), first_node(-1),
   858         first_free_node(-1), arcs(), first_free_arc(-1) {}
   859 
   860 
   861     int maxNodeId() const { return nodes.size()-1; }
   862     int maxEdgeId() const { return arcs.size() / 2 - 1; }
   863     int maxArcId() const { return arcs.size()-1; }
   864 
   865     Node source(Arc e) const { return Node(arcs[e.id ^ 1].target); }
   866     Node target(Arc e) const { return Node(arcs[e.id].target); }
   867 
   868     Node u(Edge e) const { return Node(arcs[2 * e.id].target); }
   869     Node v(Edge e) const { return Node(arcs[2 * e.id + 1].target); }
   870 
   871     static bool direction(Arc e) {
   872       return (e.id & 1) == 1;
   873     }
   874 
   875     static Arc direct(Edge e, bool d) {
   876       return Arc(e.id * 2 + (d ? 1 : 0));
   877     }
   878 
   879     void first(Node& node) const {
   880       node.id = first_node;
   881     }
   882 
   883     void next(Node& node) const {
   884       node.id = nodes[node.id].next;
   885     }
   886 
   887     void first(Arc& e) const {
   888       int n = first_node;
   889       while (n != -1 && nodes[n].first_out == -1) {
   890         n = nodes[n].next;
   891       }
   892       e.id = (n == -1) ? -1 : nodes[n].first_out;
   893     }
   894 
   895     void next(Arc& e) const {
   896       if (arcs[e.id].next_out != -1) {
   897         e.id = arcs[e.id].next_out;
   898       } else {
   899         int n = nodes[arcs[e.id ^ 1].target].next;
   900         while(n != -1 && nodes[n].first_out == -1) {
   901           n = nodes[n].next;
   902         }
   903         e.id = (n == -1) ? -1 : nodes[n].first_out;
   904       }
   905     }
   906 
   907     void first(Edge& e) const {
   908       int n = first_node;
   909       while (n != -1) {
   910         e.id = nodes[n].first_out;
   911         while ((e.id & 1) != 1) {
   912           e.id = arcs[e.id].next_out;
   913         }
   914         if (e.id != -1) {
   915           e.id /= 2;
   916           return;
   917         }
   918         n = nodes[n].next;
   919       }
   920       e.id = -1;
   921     }
   922 
   923     void next(Edge& e) const {
   924       int n = arcs[e.id * 2].target;
   925       e.id = arcs[(e.id * 2) | 1].next_out;
   926       while ((e.id & 1) != 1) {
   927         e.id = arcs[e.id].next_out;
   928       }
   929       if (e.id != -1) {
   930         e.id /= 2;
   931         return;
   932       }
   933       n = nodes[n].next;
   934       while (n != -1) {
   935         e.id = nodes[n].first_out;
   936         while ((e.id & 1) != 1) {
   937           e.id = arcs[e.id].next_out;
   938         }
   939         if (e.id != -1) {
   940           e.id /= 2;
   941           return;
   942         }
   943         n = nodes[n].next;
   944       }
   945       e.id = -1;
   946     }
   947 
   948     void firstOut(Arc &e, const Node& v) const {
   949       e.id = nodes[v.id].first_out;
   950     }
   951     void nextOut(Arc &e) const {
   952       e.id = arcs[e.id].next_out;
   953     }
   954 
   955     void firstIn(Arc &e, const Node& v) const {
   956       e.id = ((nodes[v.id].first_out) ^ 1);
   957       if (e.id == -2) e.id = -1;
   958     }
   959     void nextIn(Arc &e) const {
   960       e.id = ((arcs[e.id ^ 1].next_out) ^ 1);
   961       if (e.id == -2) e.id = -1;
   962     }
   963 
   964     void firstInc(Edge &e, bool& d, const Node& v) const {
   965       int a = nodes[v.id].first_out;
   966       if (a != -1 ) {
   967         e.id = a / 2;
   968         d = ((a & 1) == 1);
   969       } else {
   970         e.id = -1;
   971         d = true;
   972       }
   973     }
   974     void nextInc(Edge &e, bool& d) const {
   975       int a = (arcs[(e.id * 2) | (d ? 1 : 0)].next_out);
   976       if (a != -1 ) {
   977         e.id = a / 2;
   978         d = ((a & 1) == 1);
   979       } else {
   980         e.id = -1;
   981         d = true;
   982       }
   983     }
   984 
   985     static int id(Node v) { return v.id; }
   986     static int id(Arc e) { return e.id; }
   987     static int id(Edge e) { return e.id; }
   988 
   989     static Node nodeFromId(int id) { return Node(id);}
   990     static Arc arcFromId(int id) { return Arc(id);}
   991     static Edge edgeFromId(int id) { return Edge(id);}
   992 
   993     bool valid(Node n) const {
   994       return n.id >= 0 && n.id < static_cast<int>(nodes.size()) &&
   995         nodes[n.id].prev != -2;
   996     }
   997 
   998     bool valid(Arc a) const {
   999       return a.id >= 0 && a.id < static_cast<int>(arcs.size()) &&
  1000         arcs[a.id].prev_out != -2;
  1001     }
  1002 
  1003     bool valid(Edge e) const {
  1004       return e.id >= 0 && 2 * e.id < static_cast<int>(arcs.size()) &&
  1005         arcs[2 * e.id].prev_out != -2;
  1006     }
  1007 
  1008     Node addNode() {
  1009       int n;
  1010 
  1011       if(first_free_node==-1) {
  1012         n = nodes.size();
  1013         nodes.push_back(NodeT());
  1014       } else {
  1015         n = first_free_node;
  1016         first_free_node = nodes[n].next;
  1017       }
  1018 
  1019       nodes[n].next = first_node;
  1020       if (first_node != -1) nodes[first_node].prev = n;
  1021       first_node = n;
  1022       nodes[n].prev = -1;
  1023 
  1024       nodes[n].first_out = -1;
  1025 
  1026       return Node(n);
  1027     }
  1028 
  1029     Edge addEdge(Node u, Node v) {
  1030       int n;
  1031 
  1032       if (first_free_arc == -1) {
  1033         n = arcs.size();
  1034         arcs.push_back(ArcT());
  1035         arcs.push_back(ArcT());
  1036       } else {
  1037         n = first_free_arc;
  1038         first_free_arc = arcs[n].next_out;
  1039       }
  1040 
  1041       arcs[n].target = u.id;
  1042       arcs[n | 1].target = v.id;
  1043 
  1044       arcs[n].next_out = nodes[v.id].first_out;
  1045       if (nodes[v.id].first_out != -1) {
  1046         arcs[nodes[v.id].first_out].prev_out = n;
  1047       }
  1048       arcs[n].prev_out = -1;
  1049       nodes[v.id].first_out = n;
  1050 
  1051       arcs[n | 1].next_out = nodes[u.id].first_out;
  1052       if (nodes[u.id].first_out != -1) {
  1053         arcs[nodes[u.id].first_out].prev_out = (n | 1);
  1054       }
  1055       arcs[n | 1].prev_out = -1;
  1056       nodes[u.id].first_out = (n | 1);
  1057 
  1058       return Edge(n / 2);
  1059     }
  1060 
  1061     void erase(const Node& node) {
  1062       int n = node.id;
  1063 
  1064       if(nodes[n].next != -1) {
  1065         nodes[nodes[n].next].prev = nodes[n].prev;
  1066       }
  1067 
  1068       if(nodes[n].prev != -1) {
  1069         nodes[nodes[n].prev].next = nodes[n].next;
  1070       } else {
  1071         first_node = nodes[n].next;
  1072       }
  1073 
  1074       nodes[n].next = first_free_node;
  1075       first_free_node = n;
  1076       nodes[n].prev = -2;
  1077     }
  1078 
  1079     void erase(const Edge& edge) {
  1080       int n = edge.id * 2;
  1081 
  1082       if (arcs[n].next_out != -1) {
  1083         arcs[arcs[n].next_out].prev_out = arcs[n].prev_out;
  1084       }
  1085 
  1086       if (arcs[n].prev_out != -1) {
  1087         arcs[arcs[n].prev_out].next_out = arcs[n].next_out;
  1088       } else {
  1089         nodes[arcs[n | 1].target].first_out = arcs[n].next_out;
  1090       }
  1091 
  1092       if (arcs[n | 1].next_out != -1) {
  1093         arcs[arcs[n | 1].next_out].prev_out = arcs[n | 1].prev_out;
  1094       }
  1095 
  1096       if (arcs[n | 1].prev_out != -1) {
  1097         arcs[arcs[n | 1].prev_out].next_out = arcs[n | 1].next_out;
  1098       } else {
  1099         nodes[arcs[n].target].first_out = arcs[n | 1].next_out;
  1100       }
  1101 
  1102       arcs[n].next_out = first_free_arc;
  1103       first_free_arc = n;
  1104       arcs[n].prev_out = -2;
  1105       arcs[n | 1].prev_out = -2;
  1106 
  1107     }
  1108 
  1109     void clear() {
  1110       arcs.clear();
  1111       nodes.clear();
  1112       first_node = first_free_node = first_free_arc = -1;
  1113     }
  1114 
  1115   protected:
  1116 
  1117     void changeV(Edge e, Node n) {
  1118       if(arcs[2 * e.id].next_out != -1) {
  1119         arcs[arcs[2 * e.id].next_out].prev_out = arcs[2 * e.id].prev_out;
  1120       }
  1121       if(arcs[2 * e.id].prev_out != -1) {
  1122         arcs[arcs[2 * e.id].prev_out].next_out =
  1123           arcs[2 * e.id].next_out;
  1124       } else {
  1125         nodes[arcs[(2 * e.id) | 1].target].first_out =
  1126           arcs[2 * e.id].next_out;
  1127       }
  1128 
  1129       if (nodes[n.id].first_out != -1) {
  1130         arcs[nodes[n.id].first_out].prev_out = 2 * e.id;
  1131       }
  1132       arcs[(2 * e.id) | 1].target = n.id;
  1133       arcs[2 * e.id].prev_out = -1;
  1134       arcs[2 * e.id].next_out = nodes[n.id].first_out;
  1135       nodes[n.id].first_out = 2 * e.id;
  1136     }
  1137 
  1138     void changeU(Edge e, Node n) {
  1139       if(arcs[(2 * e.id) | 1].next_out != -1) {
  1140         arcs[arcs[(2 * e.id) | 1].next_out].prev_out =
  1141           arcs[(2 * e.id) | 1].prev_out;
  1142       }
  1143       if(arcs[(2 * e.id) | 1].prev_out != -1) {
  1144         arcs[arcs[(2 * e.id) | 1].prev_out].next_out =
  1145           arcs[(2 * e.id) | 1].next_out;
  1146       } else {
  1147         nodes[arcs[2 * e.id].target].first_out =
  1148           arcs[(2 * e.id) | 1].next_out;
  1149       }
  1150 
  1151       if (nodes[n.id].first_out != -1) {
  1152         arcs[nodes[n.id].first_out].prev_out = ((2 * e.id) | 1);
  1153       }
  1154       arcs[2 * e.id].target = n.id;
  1155       arcs[(2 * e.id) | 1].prev_out = -1;
  1156       arcs[(2 * e.id) | 1].next_out = nodes[n.id].first_out;
  1157       nodes[n.id].first_out = ((2 * e.id) | 1);
  1158     }
  1159 
  1160   };
  1161 
  1162   typedef GraphExtender<ListGraphBase> ExtendedListGraphBase;
  1163 
  1164 
  1165   /// \addtogroup graphs
  1166   /// @{
  1167 
  1168   ///A general undirected graph structure.
  1169 
  1170   ///\ref ListGraph is a simple and fast <em>undirected graph</em>
  1171   ///implementation based on static linked lists that are stored in
  1172   ///\c std::vector structures.
  1173   ///
  1174   ///It conforms to the \ref concepts::Graph "Graph concept" and it
  1175   ///also provides several useful additional functionalities.
  1176   ///Most of the member functions and nested classes are documented
  1177   ///only in the concept class.
  1178   ///
  1179   ///An important extra feature of this graph implementation is that
  1180   ///its maps are real \ref concepts::ReferenceMap "reference map"s.
  1181   ///
  1182   ///\sa concepts::Graph
  1183 
  1184   class ListGraph : public ExtendedListGraphBase {
  1185   private:
  1186     ///ListGraph is \e not copy constructible. Use copyGraph() instead.
  1187 
  1188     ///ListGraph is \e not copy constructible. Use copyGraph() instead.
  1189     ///
  1190     ListGraph(const ListGraph &) :ExtendedListGraphBase()  {};
  1191     ///\brief Assignment of ListGraph to another one is \e not allowed.
  1192     ///Use copyGraph() instead.
  1193 
  1194     ///Assignment of ListGraph to another one is \e not allowed.
  1195     ///Use copyGraph() instead.
  1196     void operator=(const ListGraph &) {}
  1197   public:
  1198     /// Constructor
  1199 
  1200     /// Constructor.
  1201     ///
  1202     ListGraph() {}
  1203 
  1204     typedef ExtendedListGraphBase Parent;
  1205 
  1206     typedef Parent::OutArcIt IncEdgeIt;
  1207 
  1208     /// \brief Add a new node to the graph.
  1209     ///
  1210     /// Add a new node to the graph.
  1211     /// \return the new node.
  1212     Node addNode() { return Parent::addNode(); }
  1213 
  1214     /// \brief Add a new edge to the graph.
  1215     ///
  1216     /// Add a new edge to the graph with source node \c s
  1217     /// and target node \c t.
  1218     /// \return the new edge.
  1219     Edge addEdge(const Node& s, const Node& t) {
  1220       return Parent::addEdge(s, t);
  1221     }
  1222 
  1223     /// \brief Erase a node from the graph.
  1224     ///
  1225     /// Erase a node from the graph.
  1226     ///
  1227     void erase(const Node& n) { Parent::erase(n); }
  1228 
  1229     /// \brief Erase an edge from the graph.
  1230     ///
  1231     /// Erase an edge from the graph.
  1232     ///
  1233     void erase(const Edge& e) { Parent::erase(e); }
  1234     /// Node validity check
  1235 
  1236     /// This function gives back true if the given node is valid,
  1237     /// ie. it is a real node of the graph.
  1238     ///
  1239     /// \warning A Node pointing to a removed item
  1240     /// could become valid again later if new nodes are
  1241     /// added to the graph.
  1242     bool valid(Node n) const { return Parent::valid(n); }
  1243     /// Arc validity check
  1244 
  1245     /// This function gives back true if the given arc is valid,
  1246     /// ie. it is a real arc of the graph.
  1247     ///
  1248     /// \warning An Arc pointing to a removed item
  1249     /// could become valid again later if new edges are
  1250     /// added to the graph.
  1251     bool valid(Arc a) const { return Parent::valid(a); }
  1252     /// Edge validity check
  1253 
  1254     /// This function gives back true if the given edge is valid,
  1255     /// ie. it is a real arc of the graph.
  1256     ///
  1257     /// \warning A Edge pointing to a removed item
  1258     /// could become valid again later if new edges are
  1259     /// added to the graph.
  1260     bool valid(Edge e) const { return Parent::valid(e); }
  1261     /// \brief Change the end \c u of \c e to \c n
  1262     ///
  1263     /// This function changes the end \c u of \c e to node \c n.
  1264     ///
  1265     ///\note The <tt>EdgeIt</tt>s and <tt>ArcIt</tt>s referencing the
  1266     ///changed edge are invalidated and if the changed node is the
  1267     ///base node of an iterator then this iterator is also
  1268     ///invalidated.
  1269     ///
  1270     ///\warning This functionality cannot be used together with the
  1271     ///Snapshot feature.
  1272     void changeU(Edge e, Node n) {
  1273       Parent::changeU(e,n);
  1274     }
  1275     /// \brief Change the end \c v of \c e to \c n
  1276     ///
  1277     /// This function changes the end \c v of \c e to \c n.
  1278     ///
  1279     ///\note The <tt>EdgeIt</tt>s referencing the changed edge remain
  1280     ///valid, however <tt>ArcIt</tt>s and if the changed node is the
  1281     ///base node of an iterator then this iterator is invalidated.
  1282     ///
  1283     ///\warning This functionality cannot be used together with the
  1284     ///Snapshot feature.
  1285     void changeV(Edge e, Node n) {
  1286       Parent::changeV(e,n);
  1287     }
  1288     /// \brief Contract two nodes.
  1289     ///
  1290     /// This function contracts two nodes.
  1291     /// Node \p b will be removed but instead of deleting
  1292     /// its neighboring arcs, they will be joined to \p a.
  1293     /// The last parameter \p r controls whether to remove loops. \c true
  1294     /// means that loops will be removed.
  1295     ///
  1296     /// \note The <tt>ArcIt</tt>s referencing a moved arc remain
  1297     /// valid.
  1298     ///
  1299     ///\warning This functionality cannot be used together with the
  1300     ///Snapshot feature.
  1301     void contract(Node a, Node b, bool r = true) {
  1302       for(IncEdgeIt e(*this, b); e!=INVALID;) {
  1303         IncEdgeIt f = e; ++f;
  1304         if (r && runningNode(e) == a) {
  1305           erase(e);
  1306         } else if (u(e) == b) {
  1307           changeU(e, a);
  1308         } else {
  1309           changeV(e, a);
  1310         }
  1311         e = f;
  1312       }
  1313       erase(b);
  1314     }
  1315 
  1316 
  1317     /// \brief Class to make a snapshot of the graph and restore
  1318     /// it later.
  1319     ///
  1320     /// Class to make a snapshot of the graph and restore it later.
  1321     ///
  1322     /// The newly added nodes and edges can be removed
  1323     /// using the restore() function.
  1324     ///
  1325     /// \warning Edge and node deletions and other modifications
  1326     /// (e.g. changing nodes of edges, contracting nodes) cannot be
  1327     /// restored. These events invalidate the snapshot.
  1328     class Snapshot {
  1329     protected:
  1330 
  1331       typedef Parent::NodeNotifier NodeNotifier;
  1332 
  1333       class NodeObserverProxy : public NodeNotifier::ObserverBase {
  1334       public:
  1335 
  1336         NodeObserverProxy(Snapshot& _snapshot)
  1337           : snapshot(_snapshot) {}
  1338 
  1339         using NodeNotifier::ObserverBase::attach;
  1340         using NodeNotifier::ObserverBase::detach;
  1341         using NodeNotifier::ObserverBase::attached;
  1342 
  1343       protected:
  1344 
  1345         virtual void add(const Node& node) {
  1346           snapshot.addNode(node);
  1347         }
  1348         virtual void add(const std::vector<Node>& nodes) {
  1349           for (int i = nodes.size() - 1; i >= 0; ++i) {
  1350             snapshot.addNode(nodes[i]);
  1351           }
  1352         }
  1353         virtual void erase(const Node& node) {
  1354           snapshot.eraseNode(node);
  1355         }
  1356         virtual void erase(const std::vector<Node>& nodes) {
  1357           for (int i = 0; i < int(nodes.size()); ++i) {
  1358             snapshot.eraseNode(nodes[i]);
  1359           }
  1360         }
  1361         virtual void build() {
  1362           Node node;
  1363           std::vector<Node> nodes;
  1364           for (notifier()->first(node); node != INVALID;
  1365                notifier()->next(node)) {
  1366             nodes.push_back(node);
  1367           }
  1368           for (int i = nodes.size() - 1; i >= 0; --i) {
  1369             snapshot.addNode(nodes[i]);
  1370           }
  1371         }
  1372         virtual void clear() {
  1373           Node node;
  1374           for (notifier()->first(node); node != INVALID;
  1375                notifier()->next(node)) {
  1376             snapshot.eraseNode(node);
  1377           }
  1378         }
  1379 
  1380         Snapshot& snapshot;
  1381       };
  1382 
  1383       class EdgeObserverProxy : public EdgeNotifier::ObserverBase {
  1384       public:
  1385 
  1386         EdgeObserverProxy(Snapshot& _snapshot)
  1387           : snapshot(_snapshot) {}
  1388 
  1389         using EdgeNotifier::ObserverBase::attach;
  1390         using EdgeNotifier::ObserverBase::detach;
  1391         using EdgeNotifier::ObserverBase::attached;
  1392 
  1393       protected:
  1394 
  1395         virtual void add(const Edge& edge) {
  1396           snapshot.addEdge(edge);
  1397         }
  1398         virtual void add(const std::vector<Edge>& edges) {
  1399           for (int i = edges.size() - 1; i >= 0; ++i) {
  1400             snapshot.addEdge(edges[i]);
  1401           }
  1402         }
  1403         virtual void erase(const Edge& edge) {
  1404           snapshot.eraseEdge(edge);
  1405         }
  1406         virtual void erase(const std::vector<Edge>& edges) {
  1407           for (int i = 0; i < int(edges.size()); ++i) {
  1408             snapshot.eraseEdge(edges[i]);
  1409           }
  1410         }
  1411         virtual void build() {
  1412           Edge edge;
  1413           std::vector<Edge> edges;
  1414           for (notifier()->first(edge); edge != INVALID;
  1415                notifier()->next(edge)) {
  1416             edges.push_back(edge);
  1417           }
  1418           for (int i = edges.size() - 1; i >= 0; --i) {
  1419             snapshot.addEdge(edges[i]);
  1420           }
  1421         }
  1422         virtual void clear() {
  1423           Edge edge;
  1424           for (notifier()->first(edge); edge != INVALID;
  1425                notifier()->next(edge)) {
  1426             snapshot.eraseEdge(edge);
  1427           }
  1428         }
  1429 
  1430         Snapshot& snapshot;
  1431       };
  1432 
  1433       ListGraph *graph;
  1434 
  1435       NodeObserverProxy node_observer_proxy;
  1436       EdgeObserverProxy edge_observer_proxy;
  1437 
  1438       std::list<Node> added_nodes;
  1439       std::list<Edge> added_edges;
  1440 
  1441 
  1442       void addNode(const Node& node) {
  1443         added_nodes.push_front(node);
  1444       }
  1445       void eraseNode(const Node& node) {
  1446         std::list<Node>::iterator it =
  1447           std::find(added_nodes.begin(), added_nodes.end(), node);
  1448         if (it == added_nodes.end()) {
  1449           clear();
  1450           edge_observer_proxy.detach();
  1451           throw NodeNotifier::ImmediateDetach();
  1452         } else {
  1453           added_nodes.erase(it);
  1454         }
  1455       }
  1456 
  1457       void addEdge(const Edge& edge) {
  1458         added_edges.push_front(edge);
  1459       }
  1460       void eraseEdge(const Edge& edge) {
  1461         std::list<Edge>::iterator it =
  1462           std::find(added_edges.begin(), added_edges.end(), edge);
  1463         if (it == added_edges.end()) {
  1464           clear();
  1465           node_observer_proxy.detach();
  1466           throw EdgeNotifier::ImmediateDetach();
  1467         } else {
  1468           added_edges.erase(it);
  1469         }
  1470       }
  1471 
  1472       void attach(ListGraph &_graph) {
  1473         graph = &_graph;
  1474         node_observer_proxy.attach(graph->notifier(Node()));
  1475         edge_observer_proxy.attach(graph->notifier(Edge()));
  1476       }
  1477 
  1478       void detach() {
  1479         node_observer_proxy.detach();
  1480         edge_observer_proxy.detach();
  1481       }
  1482 
  1483       bool attached() const {
  1484         return node_observer_proxy.attached();
  1485       }
  1486 
  1487       void clear() {
  1488         added_nodes.clear();
  1489         added_edges.clear();
  1490       }
  1491 
  1492     public:
  1493 
  1494       /// \brief Default constructor.
  1495       ///
  1496       /// Default constructor.
  1497       /// To actually make a snapshot you must call save().
  1498       Snapshot()
  1499         : graph(0), node_observer_proxy(*this),
  1500           edge_observer_proxy(*this) {}
  1501 
  1502       /// \brief Constructor that immediately makes a snapshot.
  1503       ///
  1504       /// This constructor immediately makes a snapshot of the graph.
  1505       /// \param _graph The graph we make a snapshot of.
  1506       Snapshot(ListGraph &_graph)
  1507         : node_observer_proxy(*this),
  1508           edge_observer_proxy(*this) {
  1509         attach(_graph);
  1510       }
  1511 
  1512       /// \brief Make a snapshot.
  1513       ///
  1514       /// Make a snapshot of the graph.
  1515       ///
  1516       /// This function can be called more than once. In case of a repeated
  1517       /// call, the previous snapshot gets lost.
  1518       /// \param _graph The graph we make the snapshot of.
  1519       void save(ListGraph &_graph) {
  1520         if (attached()) {
  1521           detach();
  1522           clear();
  1523         }
  1524         attach(_graph);
  1525       }
  1526 
  1527       /// \brief Undo the changes until the last snapshot.
  1528       //
  1529       /// Undo the changes until the last snapshot created by save().
  1530       void restore() {
  1531         detach();
  1532         for(std::list<Edge>::iterator it = added_edges.begin();
  1533             it != added_edges.end(); ++it) {
  1534           graph->erase(*it);
  1535         }
  1536         for(std::list<Node>::iterator it = added_nodes.begin();
  1537             it != added_nodes.end(); ++it) {
  1538           graph->erase(*it);
  1539         }
  1540         clear();
  1541       }
  1542 
  1543       /// \brief Gives back true when the snapshot is valid.
  1544       ///
  1545       /// Gives back true when the snapshot is valid.
  1546       bool valid() const {
  1547         return attached();
  1548       }
  1549     };
  1550   };
  1551 
  1552   /// @}
  1553 } //namespace lemon
  1554 
  1555 
  1556 #endif