lemon/list_graph.h
author Alpar Juttner <alpar@cs.elte.hu>
Wed, 17 Sep 2008 15:04:21 +0100
changeset 264 b6b9e7576af7
parent 238 79643f6e8c52
parent 235 b46d2787e9c2
child 280 e7f8647ce760
permissions -rw-r--r--
Merge
     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 together with the
   505     ///Snapshot feature.
   506     ///
   507     ///\todo It could be implemented in a bit faster way.
   508     Node split(Node n, bool connect = true) {
   509       Node b = addNode();
   510       for(OutArcIt e(*this,n);e!=INVALID;) {
   511         OutArcIt f=e;
   512         ++f;
   513         changeSource(e,b);
   514         e=f;
   515       }
   516       if (connect) addArc(n,b);
   517       return b;
   518     }
   519 
   520     ///Split an arc.
   521 
   522     ///This function splits an arc. First a new node \c b is added to
   523     ///the digraph, then the original arc is re-targeted to \c
   524     ///b. Finally an arc from \c b to the original target is added.
   525     ///
   526     ///\return The newly created node.
   527     ///
   528     ///\warning This functionality cannot be used together with the
   529     ///Snapshot feature.
   530     Node split(Arc e) {
   531       Node b = addNode();
   532       addArc(b,target(e));
   533       changeTarget(e,b);
   534       return b;
   535     }
   536 
   537     /// \brief Class to make a snapshot of the digraph and restore
   538     /// it later.
   539     ///
   540     /// Class to make a snapshot of the digraph and restore it later.
   541     ///
   542     /// The newly added nodes and arcs can be removed using the
   543     /// restore() function.
   544     ///
   545     /// \warning Arc and node deletions and other modifications (e.g.
   546     /// contracting, splitting, reversing arcs or nodes) cannot be
   547     /// restored. These events invalidate the snapshot.
   548     class Snapshot {
   549     protected:
   550 
   551       typedef Parent::NodeNotifier NodeNotifier;
   552 
   553       class NodeObserverProxy : public NodeNotifier::ObserverBase {
   554       public:
   555 
   556         NodeObserverProxy(Snapshot& _snapshot)
   557           : snapshot(_snapshot) {}
   558 
   559         using NodeNotifier::ObserverBase::attach;
   560         using NodeNotifier::ObserverBase::detach;
   561         using NodeNotifier::ObserverBase::attached;
   562 
   563       protected:
   564 
   565         virtual void add(const Node& node) {
   566           snapshot.addNode(node);
   567         }
   568         virtual void add(const std::vector<Node>& nodes) {
   569           for (int i = nodes.size() - 1; i >= 0; ++i) {
   570             snapshot.addNode(nodes[i]);
   571           }
   572         }
   573         virtual void erase(const Node& node) {
   574           snapshot.eraseNode(node);
   575         }
   576         virtual void erase(const std::vector<Node>& nodes) {
   577           for (int i = 0; i < int(nodes.size()); ++i) {
   578             snapshot.eraseNode(nodes[i]);
   579           }
   580         }
   581         virtual void build() {
   582           Node node;
   583           std::vector<Node> nodes;
   584           for (notifier()->first(node); node != INVALID;
   585                notifier()->next(node)) {
   586             nodes.push_back(node);
   587           }
   588           for (int i = nodes.size() - 1; i >= 0; --i) {
   589             snapshot.addNode(nodes[i]);
   590           }
   591         }
   592         virtual void clear() {
   593           Node node;
   594           for (notifier()->first(node); node != INVALID;
   595                notifier()->next(node)) {
   596             snapshot.eraseNode(node);
   597           }
   598         }
   599 
   600         Snapshot& snapshot;
   601       };
   602 
   603       class ArcObserverProxy : public ArcNotifier::ObserverBase {
   604       public:
   605 
   606         ArcObserverProxy(Snapshot& _snapshot)
   607           : snapshot(_snapshot) {}
   608 
   609         using ArcNotifier::ObserverBase::attach;
   610         using ArcNotifier::ObserverBase::detach;
   611         using ArcNotifier::ObserverBase::attached;
   612 
   613       protected:
   614 
   615         virtual void add(const Arc& arc) {
   616           snapshot.addArc(arc);
   617         }
   618         virtual void add(const std::vector<Arc>& arcs) {
   619           for (int i = arcs.size() - 1; i >= 0; ++i) {
   620             snapshot.addArc(arcs[i]);
   621           }
   622         }
   623         virtual void erase(const Arc& arc) {
   624           snapshot.eraseArc(arc);
   625         }
   626         virtual void erase(const std::vector<Arc>& arcs) {
   627           for (int i = 0; i < int(arcs.size()); ++i) {
   628             snapshot.eraseArc(arcs[i]);
   629           }
   630         }
   631         virtual void build() {
   632           Arc arc;
   633           std::vector<Arc> arcs;
   634           for (notifier()->first(arc); arc != INVALID;
   635                notifier()->next(arc)) {
   636             arcs.push_back(arc);
   637           }
   638           for (int i = arcs.size() - 1; i >= 0; --i) {
   639             snapshot.addArc(arcs[i]);
   640           }
   641         }
   642         virtual void clear() {
   643           Arc arc;
   644           for (notifier()->first(arc); arc != INVALID;
   645                notifier()->next(arc)) {
   646             snapshot.eraseArc(arc);
   647           }
   648         }
   649 
   650         Snapshot& snapshot;
   651       };
   652 
   653       ListDigraph *digraph;
   654 
   655       NodeObserverProxy node_observer_proxy;
   656       ArcObserverProxy arc_observer_proxy;
   657 
   658       std::list<Node> added_nodes;
   659       std::list<Arc> added_arcs;
   660 
   661 
   662       void addNode(const Node& node) {
   663         added_nodes.push_front(node);
   664       }
   665       void eraseNode(const Node& node) {
   666         std::list<Node>::iterator it =
   667           std::find(added_nodes.begin(), added_nodes.end(), node);
   668         if (it == added_nodes.end()) {
   669           clear();
   670           arc_observer_proxy.detach();
   671           throw NodeNotifier::ImmediateDetach();
   672         } else {
   673           added_nodes.erase(it);
   674         }
   675       }
   676 
   677       void addArc(const Arc& arc) {
   678         added_arcs.push_front(arc);
   679       }
   680       void eraseArc(const Arc& arc) {
   681         std::list<Arc>::iterator it =
   682           std::find(added_arcs.begin(), added_arcs.end(), arc);
   683         if (it == added_arcs.end()) {
   684           clear();
   685           node_observer_proxy.detach();
   686           throw ArcNotifier::ImmediateDetach();
   687         } else {
   688           added_arcs.erase(it);
   689         }
   690       }
   691 
   692       void attach(ListDigraph &_digraph) {
   693         digraph = &_digraph;
   694         node_observer_proxy.attach(digraph->notifier(Node()));
   695         arc_observer_proxy.attach(digraph->notifier(Arc()));
   696       }
   697 
   698       void detach() {
   699         node_observer_proxy.detach();
   700         arc_observer_proxy.detach();
   701       }
   702 
   703       bool attached() const {
   704         return node_observer_proxy.attached();
   705       }
   706 
   707       void clear() {
   708         added_nodes.clear();
   709         added_arcs.clear();
   710       }
   711 
   712     public:
   713 
   714       /// \brief Default constructor.
   715       ///
   716       /// Default constructor.
   717       /// To actually make a snapshot you must call save().
   718       Snapshot()
   719         : digraph(0), node_observer_proxy(*this),
   720           arc_observer_proxy(*this) {}
   721 
   722       /// \brief Constructor that immediately makes a snapshot.
   723       ///
   724       /// This constructor immediately makes a snapshot of the digraph.
   725       /// \param _digraph The digraph we make a snapshot of.
   726       Snapshot(ListDigraph &_digraph)
   727         : node_observer_proxy(*this),
   728           arc_observer_proxy(*this) {
   729         attach(_digraph);
   730       }
   731 
   732       /// \brief Make a snapshot.
   733       ///
   734       /// Make a snapshot of the digraph.
   735       ///
   736       /// This function can be called more than once. In case of a repeated
   737       /// call, the previous snapshot gets lost.
   738       /// \param _digraph The digraph we make the snapshot of.
   739       void save(ListDigraph &_digraph) {
   740         if (attached()) {
   741           detach();
   742           clear();
   743         }
   744         attach(_digraph);
   745       }
   746 
   747       /// \brief Undo the changes until the last snapshot.
   748       //
   749       /// Undo the changes until the last snapshot created by save().
   750       void restore() {
   751         detach();
   752         for(std::list<Arc>::iterator it = added_arcs.begin();
   753             it != added_arcs.end(); ++it) {
   754           digraph->erase(*it);
   755         }
   756         for(std::list<Node>::iterator it = added_nodes.begin();
   757             it != added_nodes.end(); ++it) {
   758           digraph->erase(*it);
   759         }
   760         clear();
   761       }
   762 
   763       /// \brief Gives back true when the snapshot is valid.
   764       ///
   765       /// Gives back true when the snapshot is valid.
   766       bool valid() const {
   767         return attached();
   768       }
   769     };
   770 
   771   };
   772 
   773   ///@}
   774 
   775   class ListGraphBase {
   776 
   777   protected:
   778 
   779     struct NodeT {
   780       int first_out;
   781       int prev, next;
   782     };
   783 
   784     struct ArcT {
   785       int target;
   786       int prev_out, next_out;
   787     };
   788 
   789     std::vector<NodeT> nodes;
   790 
   791     int first_node;
   792 
   793     int first_free_node;
   794 
   795     std::vector<ArcT> arcs;
   796 
   797     int first_free_arc;
   798 
   799   public:
   800 
   801     typedef ListGraphBase Digraph;
   802 
   803     class Node;
   804     class Arc;
   805     class Edge;
   806 
   807     class Node {
   808       friend class ListGraphBase;
   809     protected:
   810 
   811       int id;
   812       explicit Node(int pid) { id = pid;}
   813 
   814     public:
   815       Node() {}
   816       Node (Invalid) { id = -1; }
   817       bool operator==(const Node& node) const {return id == node.id;}
   818       bool operator!=(const Node& node) const {return id != node.id;}
   819       bool operator<(const Node& node) const {return id < node.id;}
   820     };
   821 
   822     class Edge {
   823       friend class ListGraphBase;
   824     protected:
   825 
   826       int id;
   827       explicit Edge(int pid) { id = pid;}
   828 
   829     public:
   830       Edge() {}
   831       Edge (Invalid) { id = -1; }
   832       bool operator==(const Edge& edge) const {return id == edge.id;}
   833       bool operator!=(const Edge& edge) const {return id != edge.id;}
   834       bool operator<(const Edge& edge) const {return id < edge.id;}
   835     };
   836 
   837     class Arc {
   838       friend class ListGraphBase;
   839     protected:
   840 
   841       int id;
   842       explicit Arc(int pid) { id = pid;}
   843 
   844     public:
   845       operator Edge() const { 
   846         return id != -1 ? edgeFromId(id / 2) : INVALID; 
   847       }
   848 
   849       Arc() {}
   850       Arc (Invalid) { id = -1; }
   851       bool operator==(const Arc& arc) const {return id == arc.id;}
   852       bool operator!=(const Arc& arc) const {return id != arc.id;}
   853       bool operator<(const Arc& arc) const {return id < arc.id;}
   854     };
   855 
   856 
   857 
   858     ListGraphBase()
   859       : nodes(), first_node(-1),
   860         first_free_node(-1), arcs(), first_free_arc(-1) {}
   861 
   862 
   863     int maxNodeId() const { return nodes.size()-1; }
   864     int maxEdgeId() const { return arcs.size() / 2 - 1; }
   865     int maxArcId() const { return arcs.size()-1; }
   866 
   867     Node source(Arc e) const { return Node(arcs[e.id ^ 1].target); }
   868     Node target(Arc e) const { return Node(arcs[e.id].target); }
   869 
   870     Node u(Edge e) const { return Node(arcs[2 * e.id].target); }
   871     Node v(Edge e) const { return Node(arcs[2 * e.id + 1].target); }
   872 
   873     static bool direction(Arc e) {
   874       return (e.id & 1) == 1;
   875     }
   876 
   877     static Arc direct(Edge e, bool d) {
   878       return Arc(e.id * 2 + (d ? 1 : 0));
   879     }
   880 
   881     void first(Node& node) const {
   882       node.id = first_node;
   883     }
   884 
   885     void next(Node& node) const {
   886       node.id = nodes[node.id].next;
   887     }
   888 
   889     void first(Arc& e) const {
   890       int n = first_node;
   891       while (n != -1 && nodes[n].first_out == -1) {
   892         n = nodes[n].next;
   893       }
   894       e.id = (n == -1) ? -1 : nodes[n].first_out;
   895     }
   896 
   897     void next(Arc& e) const {
   898       if (arcs[e.id].next_out != -1) {
   899         e.id = arcs[e.id].next_out;
   900       } else {
   901         int n = nodes[arcs[e.id ^ 1].target].next;
   902         while(n != -1 && nodes[n].first_out == -1) {
   903           n = nodes[n].next;
   904         }
   905         e.id = (n == -1) ? -1 : nodes[n].first_out;
   906       }
   907     }
   908 
   909     void first(Edge& e) const {
   910       int n = first_node;
   911       while (n != -1) {
   912         e.id = nodes[n].first_out;
   913         while ((e.id & 1) != 1) {
   914           e.id = arcs[e.id].next_out;
   915         }
   916         if (e.id != -1) {
   917           e.id /= 2;
   918           return;
   919         }
   920         n = nodes[n].next;
   921       }
   922       e.id = -1;
   923     }
   924 
   925     void next(Edge& e) const {
   926       int n = arcs[e.id * 2].target;
   927       e.id = arcs[(e.id * 2) | 1].next_out;
   928       while ((e.id & 1) != 1) {
   929         e.id = arcs[e.id].next_out;
   930       }
   931       if (e.id != -1) {
   932         e.id /= 2;
   933         return;
   934       }
   935       n = nodes[n].next;
   936       while (n != -1) {
   937         e.id = nodes[n].first_out;
   938         while ((e.id & 1) != 1) {
   939           e.id = arcs[e.id].next_out;
   940         }
   941         if (e.id != -1) {
   942           e.id /= 2;
   943           return;
   944         }
   945         n = nodes[n].next;
   946       }
   947       e.id = -1;
   948     }
   949 
   950     void firstOut(Arc &e, const Node& v) const {
   951       e.id = nodes[v.id].first_out;
   952     }
   953     void nextOut(Arc &e) const {
   954       e.id = arcs[e.id].next_out;
   955     }
   956 
   957     void firstIn(Arc &e, const Node& v) const {
   958       e.id = ((nodes[v.id].first_out) ^ 1);
   959       if (e.id == -2) e.id = -1;
   960     }
   961     void nextIn(Arc &e) const {
   962       e.id = ((arcs[e.id ^ 1].next_out) ^ 1);
   963       if (e.id == -2) e.id = -1;
   964     }
   965 
   966     void firstInc(Edge &e, bool& d, const Node& v) const {
   967       int a = nodes[v.id].first_out;
   968       if (a != -1 ) {
   969         e.id = a / 2;
   970         d = ((a & 1) == 1);
   971       } else {
   972         e.id = -1;
   973         d = true;
   974       }
   975     }
   976     void nextInc(Edge &e, bool& d) const {
   977       int a = (arcs[(e.id * 2) | (d ? 1 : 0)].next_out);
   978       if (a != -1 ) {
   979         e.id = a / 2;
   980         d = ((a & 1) == 1);
   981       } else {
   982         e.id = -1;
   983         d = true;
   984       }
   985     }
   986 
   987     static int id(Node v) { return v.id; }
   988     static int id(Arc e) { return e.id; }
   989     static int id(Edge e) { return e.id; }
   990 
   991     static Node nodeFromId(int id) { return Node(id);}
   992     static Arc arcFromId(int id) { return Arc(id);}
   993     static Edge edgeFromId(int id) { return Edge(id);}
   994 
   995     bool valid(Node n) const {
   996       return n.id >= 0 && n.id < static_cast<int>(nodes.size()) &&
   997         nodes[n.id].prev != -2;
   998     }
   999 
  1000     bool valid(Arc a) const {
  1001       return a.id >= 0 && a.id < static_cast<int>(arcs.size()) &&
  1002         arcs[a.id].prev_out != -2;
  1003     }
  1004 
  1005     bool valid(Edge e) const {
  1006       return e.id >= 0 && 2 * e.id < static_cast<int>(arcs.size()) &&
  1007         arcs[2 * e.id].prev_out != -2;
  1008     }
  1009 
  1010     Node addNode() {
  1011       int n;
  1012 
  1013       if(first_free_node==-1) {
  1014         n = nodes.size();
  1015         nodes.push_back(NodeT());
  1016       } else {
  1017         n = first_free_node;
  1018         first_free_node = nodes[n].next;
  1019       }
  1020 
  1021       nodes[n].next = first_node;
  1022       if (first_node != -1) nodes[first_node].prev = n;
  1023       first_node = n;
  1024       nodes[n].prev = -1;
  1025 
  1026       nodes[n].first_out = -1;
  1027 
  1028       return Node(n);
  1029     }
  1030 
  1031     Edge addEdge(Node u, Node v) {
  1032       int n;
  1033 
  1034       if (first_free_arc == -1) {
  1035         n = arcs.size();
  1036         arcs.push_back(ArcT());
  1037         arcs.push_back(ArcT());
  1038       } else {
  1039         n = first_free_arc;
  1040         first_free_arc = arcs[n].next_out;
  1041       }
  1042 
  1043       arcs[n].target = u.id;
  1044       arcs[n | 1].target = v.id;
  1045 
  1046       arcs[n].next_out = nodes[v.id].first_out;
  1047       if (nodes[v.id].first_out != -1) {
  1048         arcs[nodes[v.id].first_out].prev_out = n;
  1049       }
  1050       arcs[n].prev_out = -1;
  1051       nodes[v.id].first_out = n;
  1052 
  1053       arcs[n | 1].next_out = nodes[u.id].first_out;
  1054       if (nodes[u.id].first_out != -1) {
  1055         arcs[nodes[u.id].first_out].prev_out = (n | 1);
  1056       }
  1057       arcs[n | 1].prev_out = -1;
  1058       nodes[u.id].first_out = (n | 1);
  1059 
  1060       return Edge(n / 2);
  1061     }
  1062 
  1063     void erase(const Node& node) {
  1064       int n = node.id;
  1065 
  1066       if(nodes[n].next != -1) {
  1067         nodes[nodes[n].next].prev = nodes[n].prev;
  1068       }
  1069 
  1070       if(nodes[n].prev != -1) {
  1071         nodes[nodes[n].prev].next = nodes[n].next;
  1072       } else {
  1073         first_node = nodes[n].next;
  1074       }
  1075 
  1076       nodes[n].next = first_free_node;
  1077       first_free_node = n;
  1078       nodes[n].prev = -2;
  1079     }
  1080 
  1081     void erase(const Edge& edge) {
  1082       int n = edge.id * 2;
  1083 
  1084       if (arcs[n].next_out != -1) {
  1085         arcs[arcs[n].next_out].prev_out = arcs[n].prev_out;
  1086       }
  1087 
  1088       if (arcs[n].prev_out != -1) {
  1089         arcs[arcs[n].prev_out].next_out = arcs[n].next_out;
  1090       } else {
  1091         nodes[arcs[n | 1].target].first_out = arcs[n].next_out;
  1092       }
  1093 
  1094       if (arcs[n | 1].next_out != -1) {
  1095         arcs[arcs[n | 1].next_out].prev_out = arcs[n | 1].prev_out;
  1096       }
  1097 
  1098       if (arcs[n | 1].prev_out != -1) {
  1099         arcs[arcs[n | 1].prev_out].next_out = arcs[n | 1].next_out;
  1100       } else {
  1101         nodes[arcs[n].target].first_out = arcs[n | 1].next_out;
  1102       }
  1103 
  1104       arcs[n].next_out = first_free_arc;
  1105       first_free_arc = n;
  1106       arcs[n].prev_out = -2;
  1107       arcs[n | 1].prev_out = -2;
  1108 
  1109     }
  1110 
  1111     void clear() {
  1112       arcs.clear();
  1113       nodes.clear();
  1114       first_node = first_free_node = first_free_arc = -1;
  1115     }
  1116 
  1117   protected:
  1118 
  1119     void changeV(Edge e, Node n) {
  1120       if(arcs[2 * e.id].next_out != -1) {
  1121         arcs[arcs[2 * e.id].next_out].prev_out = arcs[2 * e.id].prev_out;
  1122       }
  1123       if(arcs[2 * e.id].prev_out != -1) {
  1124         arcs[arcs[2 * e.id].prev_out].next_out =
  1125           arcs[2 * e.id].next_out;
  1126       } else {
  1127         nodes[arcs[(2 * e.id) | 1].target].first_out =
  1128           arcs[2 * e.id].next_out;
  1129       }
  1130 
  1131       if (nodes[n.id].first_out != -1) {
  1132         arcs[nodes[n.id].first_out].prev_out = 2 * e.id;
  1133       }
  1134       arcs[(2 * e.id) | 1].target = n.id;
  1135       arcs[2 * e.id].prev_out = -1;
  1136       arcs[2 * e.id].next_out = nodes[n.id].first_out;
  1137       nodes[n.id].first_out = 2 * e.id;
  1138     }
  1139 
  1140     void changeU(Edge e, Node n) {
  1141       if(arcs[(2 * e.id) | 1].next_out != -1) {
  1142         arcs[arcs[(2 * e.id) | 1].next_out].prev_out =
  1143           arcs[(2 * e.id) | 1].prev_out;
  1144       }
  1145       if(arcs[(2 * e.id) | 1].prev_out != -1) {
  1146         arcs[arcs[(2 * e.id) | 1].prev_out].next_out =
  1147           arcs[(2 * e.id) | 1].next_out;
  1148       } else {
  1149         nodes[arcs[2 * e.id].target].first_out =
  1150           arcs[(2 * e.id) | 1].next_out;
  1151       }
  1152 
  1153       if (nodes[n.id].first_out != -1) {
  1154         arcs[nodes[n.id].first_out].prev_out = ((2 * e.id) | 1);
  1155       }
  1156       arcs[2 * e.id].target = n.id;
  1157       arcs[(2 * e.id) | 1].prev_out = -1;
  1158       arcs[(2 * e.id) | 1].next_out = nodes[n.id].first_out;
  1159       nodes[n.id].first_out = ((2 * e.id) | 1);
  1160     }
  1161 
  1162   };
  1163 
  1164   typedef GraphExtender<ListGraphBase> ExtendedListGraphBase;
  1165 
  1166 
  1167   /// \addtogroup graphs
  1168   /// @{
  1169 
  1170   ///A general undirected graph structure.
  1171 
  1172   ///\ref ListGraph is a simple and fast <em>undirected graph</em>
  1173   ///implementation based on static linked lists that are stored in
  1174   ///\c std::vector structures.
  1175   ///
  1176   ///It conforms to the \ref concepts::Graph "Graph concept" and it
  1177   ///also provides several useful additional functionalities.
  1178   ///Most of the member functions and nested classes are documented
  1179   ///only in the concept class.
  1180   ///
  1181   ///An important extra feature of this graph implementation is that
  1182   ///its maps are real \ref concepts::ReferenceMap "reference map"s.
  1183   ///
  1184   ///\sa concepts::Graph
  1185 
  1186   class ListGraph : public ExtendedListGraphBase {
  1187   private:
  1188     ///ListGraph is \e not copy constructible. Use copyGraph() instead.
  1189 
  1190     ///ListGraph is \e not copy constructible. Use copyGraph() instead.
  1191     ///
  1192     ListGraph(const ListGraph &) :ExtendedListGraphBase()  {};
  1193     ///\brief Assignment of ListGraph to another one is \e not allowed.
  1194     ///Use copyGraph() instead.
  1195 
  1196     ///Assignment of ListGraph to another one is \e not allowed.
  1197     ///Use copyGraph() instead.
  1198     void operator=(const ListGraph &) {}
  1199   public:
  1200     /// Constructor
  1201 
  1202     /// Constructor.
  1203     ///
  1204     ListGraph() {}
  1205 
  1206     typedef ExtendedListGraphBase Parent;
  1207 
  1208     typedef Parent::OutArcIt IncEdgeIt;
  1209 
  1210     /// \brief Add a new node to the graph.
  1211     ///
  1212     /// Add a new node to the graph.
  1213     /// \return the new node.
  1214     Node addNode() { return Parent::addNode(); }
  1215 
  1216     /// \brief Add a new edge to the graph.
  1217     ///
  1218     /// Add a new edge to the graph with source node \c s
  1219     /// and target node \c t.
  1220     /// \return the new edge.
  1221     Edge addEdge(const Node& s, const Node& t) {
  1222       return Parent::addEdge(s, t);
  1223     }
  1224 
  1225     /// \brief Erase a node from the graph.
  1226     ///
  1227     /// Erase a node from the graph.
  1228     ///
  1229     void erase(const Node& n) { Parent::erase(n); }
  1230 
  1231     /// \brief Erase an edge from the graph.
  1232     ///
  1233     /// Erase an edge from the graph.
  1234     ///
  1235     void erase(const Edge& e) { Parent::erase(e); }
  1236     /// Node validity check
  1237 
  1238     /// This function gives back true if the given node is valid,
  1239     /// ie. it is a real node of the graph.
  1240     ///
  1241     /// \warning A Node pointing to a removed item
  1242     /// could become valid again later if new nodes are
  1243     /// added to the graph.
  1244     bool valid(Node n) const { return Parent::valid(n); }
  1245     /// Arc validity check
  1246 
  1247     /// This function gives back true if the given arc is valid,
  1248     /// ie. it is a real arc of the graph.
  1249     ///
  1250     /// \warning An Arc pointing to a removed item
  1251     /// could become valid again later if new edges are
  1252     /// added to the graph.
  1253     bool valid(Arc a) const { return Parent::valid(a); }
  1254     /// Edge validity check
  1255 
  1256     /// This function gives back true if the given edge is valid,
  1257     /// ie. it is a real arc of the graph.
  1258     ///
  1259     /// \warning A Edge pointing to a removed item
  1260     /// could become valid again later if new edges are
  1261     /// added to the graph.
  1262     bool valid(Edge e) const { return Parent::valid(e); }
  1263     /// \brief Change the end \c u of \c e to \c n
  1264     ///
  1265     /// This function changes the end \c u of \c e to node \c n.
  1266     ///
  1267     ///\note The <tt>EdgeIt</tt>s and <tt>ArcIt</tt>s referencing the
  1268     ///changed edge are invalidated and if the changed node is the
  1269     ///base node of an iterator then this iterator is also
  1270     ///invalidated.
  1271     ///
  1272     ///\warning This functionality cannot be used together with the
  1273     ///Snapshot feature.
  1274     void changeU(Edge e, Node n) {
  1275       Parent::changeU(e,n);
  1276     }
  1277     /// \brief Change the end \c v of \c e to \c n
  1278     ///
  1279     /// This function changes the end \c v of \c e to \c n.
  1280     ///
  1281     ///\note The <tt>EdgeIt</tt>s referencing the changed edge remain
  1282     ///valid, however <tt>ArcIt</tt>s and if the changed node is the
  1283     ///base node of an iterator then this iterator is invalidated.
  1284     ///
  1285     ///\warning This functionality cannot be used together with the
  1286     ///Snapshot feature.
  1287     void changeV(Edge e, Node n) {
  1288       Parent::changeV(e,n);
  1289     }
  1290     /// \brief Contract two nodes.
  1291     ///
  1292     /// This function contracts two nodes.
  1293     /// Node \p b will be removed but instead of deleting
  1294     /// its neighboring arcs, they will be joined to \p a.
  1295     /// The last parameter \p r controls whether to remove loops. \c true
  1296     /// means that loops will be removed.
  1297     ///
  1298     /// \note The <tt>ArcIt</tt>s referencing a moved arc remain
  1299     /// valid.
  1300     ///
  1301     ///\warning This functionality cannot be used together with the
  1302     ///Snapshot feature.
  1303     void contract(Node a, Node b, bool r = true) {
  1304       for(IncEdgeIt e(*this, b); e!=INVALID;) {
  1305         IncEdgeIt f = e; ++f;
  1306         if (r && runningNode(e) == a) {
  1307           erase(e);
  1308         } else if (u(e) == b) {
  1309           changeU(e, a);
  1310         } else {
  1311           changeV(e, a);
  1312         }
  1313         e = f;
  1314       }
  1315       erase(b);
  1316     }
  1317 
  1318 
  1319     /// \brief Class to make a snapshot of the graph and restore
  1320     /// it later.
  1321     ///
  1322     /// Class to make a snapshot of the graph and restore it later.
  1323     ///
  1324     /// The newly added nodes and edges can be removed
  1325     /// using the restore() function.
  1326     ///
  1327     /// \warning Edge and node deletions and other modifications
  1328     /// (e.g. changing nodes of edges, contracting nodes) cannot be
  1329     /// restored. These events invalidate the snapshot.
  1330     class Snapshot {
  1331     protected:
  1332 
  1333       typedef Parent::NodeNotifier NodeNotifier;
  1334 
  1335       class NodeObserverProxy : public NodeNotifier::ObserverBase {
  1336       public:
  1337 
  1338         NodeObserverProxy(Snapshot& _snapshot)
  1339           : snapshot(_snapshot) {}
  1340 
  1341         using NodeNotifier::ObserverBase::attach;
  1342         using NodeNotifier::ObserverBase::detach;
  1343         using NodeNotifier::ObserverBase::attached;
  1344 
  1345       protected:
  1346 
  1347         virtual void add(const Node& node) {
  1348           snapshot.addNode(node);
  1349         }
  1350         virtual void add(const std::vector<Node>& nodes) {
  1351           for (int i = nodes.size() - 1; i >= 0; ++i) {
  1352             snapshot.addNode(nodes[i]);
  1353           }
  1354         }
  1355         virtual void erase(const Node& node) {
  1356           snapshot.eraseNode(node);
  1357         }
  1358         virtual void erase(const std::vector<Node>& nodes) {
  1359           for (int i = 0; i < int(nodes.size()); ++i) {
  1360             snapshot.eraseNode(nodes[i]);
  1361           }
  1362         }
  1363         virtual void build() {
  1364           Node node;
  1365           std::vector<Node> nodes;
  1366           for (notifier()->first(node); node != INVALID;
  1367                notifier()->next(node)) {
  1368             nodes.push_back(node);
  1369           }
  1370           for (int i = nodes.size() - 1; i >= 0; --i) {
  1371             snapshot.addNode(nodes[i]);
  1372           }
  1373         }
  1374         virtual void clear() {
  1375           Node node;
  1376           for (notifier()->first(node); node != INVALID;
  1377                notifier()->next(node)) {
  1378             snapshot.eraseNode(node);
  1379           }
  1380         }
  1381 
  1382         Snapshot& snapshot;
  1383       };
  1384 
  1385       class EdgeObserverProxy : public EdgeNotifier::ObserverBase {
  1386       public:
  1387 
  1388         EdgeObserverProxy(Snapshot& _snapshot)
  1389           : snapshot(_snapshot) {}
  1390 
  1391         using EdgeNotifier::ObserverBase::attach;
  1392         using EdgeNotifier::ObserverBase::detach;
  1393         using EdgeNotifier::ObserverBase::attached;
  1394 
  1395       protected:
  1396 
  1397         virtual void add(const Edge& edge) {
  1398           snapshot.addEdge(edge);
  1399         }
  1400         virtual void add(const std::vector<Edge>& edges) {
  1401           for (int i = edges.size() - 1; i >= 0; ++i) {
  1402             snapshot.addEdge(edges[i]);
  1403           }
  1404         }
  1405         virtual void erase(const Edge& edge) {
  1406           snapshot.eraseEdge(edge);
  1407         }
  1408         virtual void erase(const std::vector<Edge>& edges) {
  1409           for (int i = 0; i < int(edges.size()); ++i) {
  1410             snapshot.eraseEdge(edges[i]);
  1411           }
  1412         }
  1413         virtual void build() {
  1414           Edge edge;
  1415           std::vector<Edge> edges;
  1416           for (notifier()->first(edge); edge != INVALID;
  1417                notifier()->next(edge)) {
  1418             edges.push_back(edge);
  1419           }
  1420           for (int i = edges.size() - 1; i >= 0; --i) {
  1421             snapshot.addEdge(edges[i]);
  1422           }
  1423         }
  1424         virtual void clear() {
  1425           Edge edge;
  1426           for (notifier()->first(edge); edge != INVALID;
  1427                notifier()->next(edge)) {
  1428             snapshot.eraseEdge(edge);
  1429           }
  1430         }
  1431 
  1432         Snapshot& snapshot;
  1433       };
  1434 
  1435       ListGraph *graph;
  1436 
  1437       NodeObserverProxy node_observer_proxy;
  1438       EdgeObserverProxy edge_observer_proxy;
  1439 
  1440       std::list<Node> added_nodes;
  1441       std::list<Edge> added_edges;
  1442 
  1443 
  1444       void addNode(const Node& node) {
  1445         added_nodes.push_front(node);
  1446       }
  1447       void eraseNode(const Node& node) {
  1448         std::list<Node>::iterator it =
  1449           std::find(added_nodes.begin(), added_nodes.end(), node);
  1450         if (it == added_nodes.end()) {
  1451           clear();
  1452           edge_observer_proxy.detach();
  1453           throw NodeNotifier::ImmediateDetach();
  1454         } else {
  1455           added_nodes.erase(it);
  1456         }
  1457       }
  1458 
  1459       void addEdge(const Edge& edge) {
  1460         added_edges.push_front(edge);
  1461       }
  1462       void eraseEdge(const Edge& edge) {
  1463         std::list<Edge>::iterator it =
  1464           std::find(added_edges.begin(), added_edges.end(), edge);
  1465         if (it == added_edges.end()) {
  1466           clear();
  1467           node_observer_proxy.detach();
  1468           throw EdgeNotifier::ImmediateDetach();
  1469         } else {
  1470           added_edges.erase(it);
  1471         }
  1472       }
  1473 
  1474       void attach(ListGraph &_graph) {
  1475         graph = &_graph;
  1476         node_observer_proxy.attach(graph->notifier(Node()));
  1477         edge_observer_proxy.attach(graph->notifier(Edge()));
  1478       }
  1479 
  1480       void detach() {
  1481         node_observer_proxy.detach();
  1482         edge_observer_proxy.detach();
  1483       }
  1484 
  1485       bool attached() const {
  1486         return node_observer_proxy.attached();
  1487       }
  1488 
  1489       void clear() {
  1490         added_nodes.clear();
  1491         added_edges.clear();
  1492       }
  1493 
  1494     public:
  1495 
  1496       /// \brief Default constructor.
  1497       ///
  1498       /// Default constructor.
  1499       /// To actually make a snapshot you must call save().
  1500       Snapshot()
  1501         : graph(0), node_observer_proxy(*this),
  1502           edge_observer_proxy(*this) {}
  1503 
  1504       /// \brief Constructor that immediately makes a snapshot.
  1505       ///
  1506       /// This constructor immediately makes a snapshot of the graph.
  1507       /// \param _graph The graph we make a snapshot of.
  1508       Snapshot(ListGraph &_graph)
  1509         : node_observer_proxy(*this),
  1510           edge_observer_proxy(*this) {
  1511         attach(_graph);
  1512       }
  1513 
  1514       /// \brief Make a snapshot.
  1515       ///
  1516       /// Make a snapshot of the graph.
  1517       ///
  1518       /// This function can be called more than once. In case of a repeated
  1519       /// call, the previous snapshot gets lost.
  1520       /// \param _graph The graph we make the snapshot of.
  1521       void save(ListGraph &_graph) {
  1522         if (attached()) {
  1523           detach();
  1524           clear();
  1525         }
  1526         attach(_graph);
  1527       }
  1528 
  1529       /// \brief Undo the changes until the last snapshot.
  1530       //
  1531       /// Undo the changes until the last snapshot created by save().
  1532       void restore() {
  1533         detach();
  1534         for(std::list<Edge>::iterator it = added_edges.begin();
  1535             it != added_edges.end(); ++it) {
  1536           graph->erase(*it);
  1537         }
  1538         for(std::list<Node>::iterator it = added_nodes.begin();
  1539             it != added_nodes.end(); ++it) {
  1540           graph->erase(*it);
  1541         }
  1542         clear();
  1543       }
  1544 
  1545       /// \brief Gives back true when the snapshot is valid.
  1546       ///
  1547       /// Gives back true when the snapshot is valid.
  1548       bool valid() const {
  1549         return attached();
  1550       }
  1551     };
  1552   };
  1553 
  1554   /// @}
  1555 } //namespace lemon
  1556 
  1557 
  1558 #endif