RhodeCode

      arcs[n].next_in = nodes[v.id].first_in;

      if(nodes[v.id].first_in != -1) {

        arcs[nodes[v.id].first_in].prev_in = n;

      }

      arcs[n].prev_in = arcs[n].prev_out = -1;

      nodes[u.id].first_out = nodes[v.id].first_in = n;

      return Arc(n);

    }

    void erase(const Node& node) {

      int n = node.id;

      if(nodes[n].next != -1) {

        nodes[nodes[n].next].prev = nodes[n].prev;

      }

      if(nodes[n].prev != -1) {

        nodes[nodes[n].prev].next = nodes[n].next;

      } else {

        first_node = nodes[n].next;

      }

      nodes[n].next = first_free_node;

      first_free_node = n;

      nodes[n].prev = -2;

    }

    void erase(const Arc& arc) {

      int n = arc.id;

      if(arcs[n].next_in!=-1) {

        arcs[arcs[n].next_in].prev_in = arcs[n].prev_in;

      }

      if(arcs[n].prev_in!=-1) {

        arcs[arcs[n].prev_in].next_in = arcs[n].next_in;

      } else {

        nodes[arcs[n].target].first_in = arcs[n].next_in;

      }

      if(arcs[n].next_out!=-1) {

        arcs[arcs[n].next_out].prev_out = arcs[n].prev_out;

      }

      if(arcs[n].prev_out!=-1) {

        arcs[arcs[n].prev_out].next_out = arcs[n].next_out;

      } else {

        nodes[arcs[n].source].first_out = arcs[n].next_out;

      }

      arcs[n].next_in = first_free_arc;

      first_free_arc = n;

      arcs[n].prev_in = -2;

    }

    void clear() {

      arcs.clear();

      nodes.clear();

      first_node = first_free_node = first_free_arc = -1;

    }

  protected:

    void changeTarget(Arc e, Node n)

    {

      if(arcs[e.id].next_in != -1)

        arcs[arcs[e.id].next_in].prev_in = arcs[e.id].prev_in;

      if(arcs[e.id].prev_in != -1)

        arcs[arcs[e.id].prev_in].next_in = arcs[e.id].next_in;

      else nodes[arcs[e.id].target].first_in = arcs[e.id].next_in;

      if (nodes[n.id].first_in != -1) {

        arcs[nodes[n.id].first_in].prev_in = e.id;

      }

      arcs[e.id].target = n.id;

      arcs[e.id].prev_in = -1;

      arcs[e.id].next_in = nodes[n.id].first_in;

      nodes[n.id].first_in = e.id;

    }

    void changeSource(Arc e, Node n)

    {

      if(arcs[e.id].next_out != -1)

        arcs[arcs[e.id].next_out].prev_out = arcs[e.id].prev_out;

      if(arcs[e.id].prev_out != -1)

        arcs[arcs[e.id].prev_out].next_out = arcs[e.id].next_out;

      else nodes[arcs[e.id].source].first_out = arcs[e.id].next_out;

      if (nodes[n.id].first_out != -1) {

        arcs[nodes[n.id].first_out].prev_out = e.id;

      }

      arcs[e.id].source = n.id;

      arcs[e.id].prev_out = -1;

      arcs[e.id].next_out = nodes[n.id].first_out;

      nodes[n.id].first_out = e.id;

    }

  };

  typedef DigraphExtender<ListDigraphBase> ExtendedListDigraphBase;

  /// \addtogroup graphs

  /// @{

  ///A general directed graph structure.

  ///\ref ListDigraph is a simple and fast <em>directed graph</em>

  ///implementation based on static linked lists that are stored in

  ///\c std::vector structures.

  ///

  ///It conforms to the \ref concepts::Digraph "Digraph concept" and it

  ///also provides several useful additional functionalities.

  ///Most of the member functions and nested classes are documented

  ///only in the concept class.

  ///

  ///An important extra feature of this digraph implementation is that

  ///its maps are real \ref concepts::ReferenceMap "reference map"s.

  ///

  ///\sa concepts::Digraph

  class ListDigraph : public ExtendedListDigraphBase {

  private:

    ///ListDigraph is \e not copy constructible. Use copyDigraph() instead.

    ///ListDigraph is \e not copy constructible. Use copyDigraph() instead.

    ///

    ListDigraph(const ListDigraph &) :ExtendedListDigraphBase() {};

    ///\brief Assignment of ListDigraph to another one is \e not allowed.

    ///Use copyDigraph() instead.

    ///Assignment of ListDigraph to another one is \e not allowed.

    ///Use copyDigraph() instead.

    void operator=(const ListDigraph &) {}

  public:

    typedef ExtendedListDigraphBase Parent;

    /// Constructor

    /// Constructor.

    ///

    ListDigraph() {}

    ///Add a new node to the digraph.

    ///Add a new node to the digraph.

    ///\return the new node.

    Node addNode() { return Parent::addNode(); }

    ///Add a new arc to the digraph.

    ///Add a new arc to the digraph with source node \c s

    ///and target node \c t.

    ///\return the new arc.

    Arc addArc(const Node& s, const Node& t) {

      return Parent::addArc(s, t);

    }

    ///\brief Erase a node from the digraph.

    ///

    ///Erase a node from the digraph.

    ///

    void erase(const Node& n) { Parent::erase(n); }

    ///\brief Erase an arc from the digraph.

    ///

    ///Erase an arc from the digraph.

    ///

    void erase(const Arc& a) { Parent::erase(a); }

    /// Node validity check

    /// This function gives back true if the given node is valid,

    /// ie. it is a real node of the graph.

    ///

    /// \warning A Node pointing to a removed item

    /// could become valid again later if new nodes are

    /// added to the graph.

    bool valid(Node n) const { return Parent::valid(n); }

    /// Arc validity check

    /// This function gives back true if the given arc is valid,

    /// ie. it is a real arc of the graph.

    ///

    /// \warning An Arc pointing to a removed item

    /// could become valid again later if new nodes are

    /// added to the graph.

    bool valid(Arc a) const { return Parent::valid(a); }

    ///

    ///\note The <tt>ArcIt</tt>s and <tt>OutArcIt</tt>s referencing

    ///the changed arc remain valid. However <tt>InArcIt</tt>s are

    ///invalidated.

    ///

    ///\warning This functionality cannot be used together with the Snapshot

    ///feature.

    }

    ///

    ///invalidated.

    ///

    ///\warning This functionality cannot be used together with the Snapshot

    ///feature.

    }

    /// Invert the direction of an arc.

    ///\note The <tt>ArcIt</tt>s referencing the changed arc remain

    ///valid. However <tt>OutArcIt</tt>s and <tt>InArcIt</tt>s are

    ///invalidated.

    ///

    ///\warning This functionality cannot be used together with the Snapshot

    ///feature.

    void reverseArc(Arc e) {

      Node t=target(e);

      changeTarget(e,source(e));

      changeSource(e,t);

    }

    /// Reserve memory for nodes.

    /// Using this function it is possible to avoid the superfluous memory

    /// allocation: if you know that the digraph you want to build will

    /// be very large (e.g. it will contain millions of nodes and/or arcs)

    /// then it is worth reserving space for this amount before starting

    /// to build the digraph.

    /// \sa reserveArc

    void reserveNode(int n) { nodes.reserve(n); };

    /// Reserve memory for arcs.

    /// Using this function it is possible to avoid the superfluous memory

    /// allocation: if you know that the digraph you want to build will

    /// be very large (e.g. it will contain millions of nodes and/or arcs)

    /// then it is worth reserving space for this amount before starting

    /// to build the digraph.

    /// \sa reserveNode

    void reserveArc(int m) { arcs.reserve(m); };

    ///Contract two nodes.

    ///This function contracts two nodes.

    ///Node \p b will be removed but instead of deleting

    ///incident arcs, they will be joined to \p a.

    ///The last parameter \p r controls whether to remove loops. \c true

    ///means that loops will be removed.

    ///

    ///\note The <tt>ArcIt</tt>s referencing a moved arc remain

    ///valid. However <tt>InArcIt</tt>s and <tt>OutArcIt</tt>s

    ///may be invalidated.

    ///

    ///\warning This functionality cannot be used together with the Snapshot

    ///feature.

    void contract(Node a, Node b, bool r = true)

    {

      for(OutArcIt e(*this,b);e!=INVALID;) {

        OutArcIt f=e;

        ++f;

        if(r && target(e)==a) erase(e);

        else changeSource(e,a);

        e=f;

      }

      for(InArcIt e(*this,b);e!=INVALID;) {

        InArcIt f=e;

        ++f;

        if(r && source(e)==a) erase(e);

        else changeTarget(e,a);

        e=f;

      }

      erase(b);

    }

    ///Split a node.

    ///This function splits a node. First a new node is added to the digraph,

    ///then the source of each outgoing arc of \c n is moved to this new node.

    ///If \c connect is \c true (this is the default value), then a new arc

    ///from \c n to the newly created node is also added.

    ///\return The newly created node.

    ///

    ///\note The <tt>ArcIt</tt>s referencing a moved arc remain

    ///valid. However <tt>InArcIt</tt>s and <tt>OutArcIt</tt>s may

    ///be invalidated.

    ///

    ///\warning This functionality cannot be used together with the

    ///Snapshot feature.

    ///

    ///\todo It could be implemented in a bit faster way.

    Node split(Node n, bool connect = true) {

      Node b = addNode();

      for(OutArcIt e(*this,n);e!=INVALID;) {

        OutArcIt f=e;

        ++f;

        changeSource(e,b);

        e=f;

      }

      if (connect) addArc(n,b);

      return b;

    }

    ///Split an arc.

    ///This function splits an arc. First a new node \c b is added to

    ///the digraph, then the original arc is re-targeted to \c

    ///b. Finally an arc from \c b to the original target is added.

    ///

    ///\return The newly created node.

    ///

    ///\warning This functionality cannot be used together with the

    ///Snapshot feature.

    Node split(Arc e) {

      Node b = addNode();

      addArc(b,target(e));

      changeTarget(e,b);

      return b;

    }

    /// \brief Class to make a snapshot of the digraph and restore

    /// it later.

    ///

    /// Class to make a snapshot of the digraph and restore it later.

    ///

    /// The newly added nodes and arcs can be removed using the

    /// restore() function.

    ///

    /// \warning Arc and node deletions and other modifications (e.g.

    /// contracting, splitting, reversing arcs or nodes) cannot be

    /// restored. These events invalidate the snapshot.

    class Snapshot {

    protected:

      typedef Parent::NodeNotifier NodeNotifier;

      class NodeObserverProxy : public NodeNotifier::ObserverBase {

      public:

        NodeObserverProxy(Snapshot& _snapshot)

          : snapshot(_snapshot) {}

        using NodeNotifier::ObserverBase::attach;

        using NodeNotifier::ObserverBase::detach;

        using NodeNotifier::ObserverBase::attached;

      protected:

        virtual void add(const Node& node) {

          snapshot.addNode(node);

        }

        virtual void add(const std::vector<Node>& nodes) {

          for (int i = nodes.size() - 1; i >= 0; ++i) {

            snapshot.addNode(nodes[i]);

          }

        }

        virtual void erase(const Node& node) {

          snapshot.eraseNode(node);

        }

        virtual void erase(const std::vector<Node>& nodes) {

          for (int i = 0; i < int(nodes.size()); ++i) {

            snapshot.eraseNode(nodes[i]);

          }

        }

        virtual void build() {

          Node node;

          std::vector<Node> nodes;

          for (notifier()->first(node); node != INVALID;

               notifier()->next(node)) {

            nodes.push_back(node);

          }

          for (int i = nodes.size() - 1; i >= 0; --i) {

            snapshot.addNode(nodes[i]);

          }

        }

        virtual void clear() {

          Node node;

          for (notifier()->first(node); node != INVALID;

               notifier()->next(node)) {

            snapshot.eraseNode(node);

          }

        }

        Snapshot& snapshot;

      };

      class ArcObserverProxy : public ArcNotifier::ObserverBase {

      public:

        ArcObserverProxy(Snapshot& _snapshot)

          : snapshot(_snapshot) {}

        using ArcNotifier::ObserverBase::attach;

        using ArcNotifier::ObserverBase::detach;

        using ArcNotifier::ObserverBase::attached;

      protected:

      e.id = arcs[(e.id * 2) | 1].next_out;

      while ((e.id & 1) != 1) {

        e.id = arcs[e.id].next_out;

      }

      if (e.id != -1) {

        e.id /= 2;

        return;

      }

      n = nodes[n].next;

      while (n != -1) {

        e.id = nodes[n].first_out;

        while ((e.id & 1) != 1) {

          e.id = arcs[e.id].next_out;

        }

        if (e.id != -1) {

          e.id /= 2;

          return;

        }

        n = nodes[n].next;

      }

      e.id = -1;

    }

    void firstOut(Arc &e, const Node& v) const {

      e.id = nodes[v.id].first_out;

    }

    void nextOut(Arc &e) const {

      e.id = arcs[e.id].next_out;

    }

    void firstIn(Arc &e, const Node& v) const {

      e.id = ((nodes[v.id].first_out) ^ 1);

      if (e.id == -2) e.id = -1;

    }

    void nextIn(Arc &e) const {

      e.id = ((arcs[e.id ^ 1].next_out) ^ 1);

      if (e.id == -2) e.id = -1;

    }

    void firstInc(Edge &e, bool& d, const Node& v) const {

      int a = nodes[v.id].first_out;

      if (a != -1 ) {

        e.id = a / 2;

        d = ((a & 1) == 1);

      } else {

        e.id = -1;

        d = true;

      }

    }

    void nextInc(Edge &e, bool& d) const {

      int a = (arcs[(e.id * 2) | (d ? 1 : 0)].next_out);

      if (a != -1 ) {

        e.id = a / 2;

        d = ((a & 1) == 1);

      } else {

        e.id = -1;

        d = true;

      }

    }

    static int id(Node v) { return v.id; }

    static int id(Arc e) { return e.id; }

    static int id(Edge e) { return e.id; }

    static Node nodeFromId(int id) { return Node(id);}

    static Arc arcFromId(int id) { return Arc(id);}

    static Edge edgeFromId(int id) { return Edge(id);}

    bool valid(Node n) const {

      return n.id >= 0 && n.id < static_cast<int>(nodes.size()) &&

        nodes[n.id].prev != -2;

    }

    bool valid(Arc a) const {

      return a.id >= 0 && a.id < static_cast<int>(arcs.size()) &&

        arcs[a.id].prev_out != -2;

    }

    bool valid(Edge e) const {

      return e.id >= 0 && 2 * e.id < static_cast<int>(arcs.size()) &&

        arcs[2 * e.id].prev_out != -2;

    }

    Node addNode() {

      int n;

      if(first_free_node==-1) {

        n = nodes.size();

        nodes.push_back(NodeT());

      } else {

        n = first_free_node;

        first_free_node = nodes[n].next;

      }

      nodes[n].next = first_node;

      if (first_node != -1) nodes[first_node].prev = n;

      first_node = n;

      nodes[n].prev = -1;

      nodes[n].first_out = -1;

      return Node(n);

    }

    Edge addEdge(Node u, Node v) {

      int n;

      if (first_free_arc == -1) {

        n = arcs.size();

        arcs.push_back(ArcT());

        arcs.push_back(ArcT());

      } else {

        n = first_free_arc;

        first_free_arc = arcs[n].next_out;

      }

      arcs[n].target = u.id;

      arcs[n | 1].target = v.id;

      arcs[n].next_out = nodes[v.id].first_out;

      if (nodes[v.id].first_out != -1) {

        arcs[nodes[v.id].first_out].prev_out = n;

      }

      arcs[n].prev_out = -1;

      nodes[v.id].first_out = n;

      arcs[n | 1].next_out = nodes[u.id].first_out;

      if (nodes[u.id].first_out != -1) {

        arcs[nodes[u.id].first_out].prev_out = (n | 1);

      }

      arcs[n | 1].prev_out = -1;

      nodes[u.id].first_out = (n | 1);

      return Edge(n / 2);

    }

    void erase(const Node& node) {

      int n = node.id;

      if(nodes[n].next != -1) {

        nodes[nodes[n].next].prev = nodes[n].prev;

      }

      if(nodes[n].prev != -1) {

        nodes[nodes[n].prev].next = nodes[n].next;

      } else {

        first_node = nodes[n].next;

      }

      nodes[n].next = first_free_node;

      first_free_node = n;

      nodes[n].prev = -2;

    }

    void erase(const Edge& edge) {

      int n = edge.id * 2;

      if (arcs[n].next_out != -1) {

        arcs[arcs[n].next_out].prev_out = arcs[n].prev_out;

      }

      if (arcs[n].prev_out != -1) {

        arcs[arcs[n].prev_out].next_out = arcs[n].next_out;

      } else {

        nodes[arcs[n | 1].target].first_out = arcs[n].next_out;

      }

      if (arcs[n | 1].next_out != -1) {

        arcs[arcs[n | 1].next_out].prev_out = arcs[n | 1].prev_out;

      }

      if (arcs[n | 1].prev_out != -1) {

        arcs[arcs[n | 1].prev_out].next_out = arcs[n | 1].next_out;

      } else {

        nodes[arcs[n].target].first_out = arcs[n | 1].next_out;

      }

      arcs[n].next_out = first_free_arc;

      first_free_arc = n;

      arcs[n].prev_out = -2;

      arcs[n | 1].prev_out = -2;

    }

    void clear() {

      arcs.clear();

      nodes.clear();

      first_node = first_free_node = first_free_arc = -1;

    }

  protected:

      if(arcs[2 * e.id].next_out != -1) {

        arcs[arcs[2 * e.id].next_out].prev_out = arcs[2 * e.id].prev_out;

      }

      if(arcs[2 * e.id].prev_out != -1) {

        arcs[arcs[2 * e.id].prev_out].next_out =

          arcs[2 * e.id].next_out;

      } else {

        nodes[arcs[(2 * e.id) | 1].target].first_out =

          arcs[2 * e.id].next_out;

      }

      if (nodes[n.id].first_out != -1) {

        arcs[nodes[n.id].first_out].prev_out = 2 * e.id;

      }

      arcs[(2 * e.id) | 1].target = n.id;

      arcs[2 * e.id].prev_out = -1;

      arcs[2 * e.id].next_out = nodes[n.id].first_out;

      nodes[n.id].first_out = 2 * e.id;

    }

      if(arcs[(2 * e.id) | 1].next_out != -1) {

        arcs[arcs[(2 * e.id) | 1].next_out].prev_out =

          arcs[(2 * e.id) | 1].prev_out;

      }

      if(arcs[(2 * e.id) | 1].prev_out != -1) {

        arcs[arcs[(2 * e.id) | 1].prev_out].next_out =

          arcs[(2 * e.id) | 1].next_out;

      } else {

        nodes[arcs[2 * e.id].target].first_out =

          arcs[(2 * e.id) | 1].next_out;

      }

      if (nodes[n.id].first_out != -1) {

        arcs[nodes[n.id].first_out].prev_out = ((2 * e.id) | 1);

      }

      arcs[2 * e.id].target = n.id;

      arcs[(2 * e.id) | 1].prev_out = -1;

      arcs[(2 * e.id) | 1].next_out = nodes[n.id].first_out;

      nodes[n.id].first_out = ((2 * e.id) | 1);

    }

  };

  typedef GraphExtender<ListGraphBase> ExtendedListGraphBase;

  /// \addtogroup graphs

  /// @{

  ///A general undirected graph structure.

  ///\ref ListGraph is a simple and fast <em>undirected graph</em>

  ///implementation based on static linked lists that are stored in

  ///\c std::vector structures.

  ///

  ///It conforms to the \ref concepts::Graph "Graph concept" and it

  ///also provides several useful additional functionalities.

  ///Most of the member functions and nested classes are documented

  ///only in the concept class.

  ///

  ///An important extra feature of this graph implementation is that

  ///its maps are real \ref concepts::ReferenceMap "reference map"s.

  ///

  ///\sa concepts::Graph

  class ListGraph : public ExtendedListGraphBase {

  private:

    ///ListGraph is \e not copy constructible. Use copyGraph() instead.

    ///ListGraph is \e not copy constructible. Use copyGraph() instead.

    ///

    ListGraph(const ListGraph &) :ExtendedListGraphBase()  {};

    ///\brief Assignment of ListGraph to another one is \e not allowed.

    ///Use copyGraph() instead.

    ///Assignment of ListGraph to another one is \e not allowed.

    ///Use copyGraph() instead.

    void operator=(const ListGraph &) {}

  public:

    /// Constructor

    /// Constructor.

    ///

    ListGraph() {}

    typedef ExtendedListGraphBase Parent;

    typedef Parent::OutArcIt IncEdgeIt;

    /// \brief Add a new node to the graph.

    ///

    /// Add a new node to the graph.

    /// \return the new node.

    Node addNode() { return Parent::addNode(); }

    /// \brief Add a new edge to the graph.

    ///

    /// Add a new edge to the graph with source node \c s

    /// and target node \c t.

    /// \return the new edge.

    Edge addEdge(const Node& s, const Node& t) {

      return Parent::addEdge(s, t);

    }

    /// \brief Erase a node from the graph.

    ///

    /// Erase a node from the graph.

    ///

    void erase(const Node& n) { Parent::erase(n); }

    /// \brief Erase an edge from the graph.

    ///

    /// Erase an edge from the graph.

    ///

    void erase(const Edge& e) { Parent::erase(e); }

    /// Node validity check

    /// This function gives back true if the given node is valid,

    /// ie. it is a real node of the graph.

    ///

    /// \warning A Node pointing to a removed item

    /// could become valid again later if new nodes are

    /// added to the graph.

    bool valid(Node n) const { return Parent::valid(n); }

    /// Arc validity check

    /// This function gives back true if the given arc is valid,

    /// ie. it is a real arc of the graph.

    ///

    /// \warning An Arc pointing to a removed item

    /// could become valid again later if new edges are

    /// added to the graph.

    bool valid(Arc a) const { return Parent::valid(a); }

    /// Edge validity check

    /// This function gives back true if the given edge is valid,

    /// ie. it is a real arc of the graph.

    ///

    /// \warning A Edge pointing to a removed item

    /// could become valid again later if new edges are

    /// added to the graph.

    bool valid(Edge e) const { return Parent::valid(e); }

    ///

    ///

    ///

    ///\warning This functionality cannot be used together with the

    ///Snapshot feature.

    }

    ///

    ///

    ///

    ///\warning This functionality cannot be used together with the

    ///Snapshot feature.

    }

    /// \brief Contract two nodes.

    ///

    /// This function contracts two nodes.

    /// Node \p b will be removed but instead of deleting

    /// its neighboring arcs, they will be joined to \p a.

    /// The last parameter \p r controls whether to remove loops. \c true

    /// means that loops will be removed.

    ///

    /// \note The <tt>ArcIt</tt>s referencing a moved arc remain

    /// valid.

    ///

    ///\warning This functionality cannot be used together with the

    ///Snapshot feature.

    void contract(Node a, Node b, bool r = true) {

      for(IncEdgeIt e(*this, b); e!=INVALID;) {

        IncEdgeIt f = e; ++f;

        if (r && runningNode(e) == a) {

          erase(e);

        } else {

        }

        e = f;

      }

      erase(b);

    }

    /// \brief Class to make a snapshot of the graph and restore

    /// it later.

    ///

    /// Class to make a snapshot of the graph and restore it later.

    ///

    /// The newly added nodes and edges can be removed

    /// using the restore() function.

    ///

    /// \warning Edge and node deletions and other modifications

    /// (e.g. changing nodes of edges, contracting nodes) cannot be

    /// restored. These events invalidate the snapshot.

    class Snapshot {

    protected:

      typedef Parent::NodeNotifier NodeNotifier;

      class NodeObserverProxy : public NodeNotifier::ObserverBase {

      public:

        NodeObserverProxy(Snapshot& _snapshot)

          : snapshot(_snapshot) {}

        using NodeNotifier::ObserverBase::attach;

        using NodeNotifier::ObserverBase::detach;

        using NodeNotifier::ObserverBase::attached;

      protected:

        virtual void add(const Node& node) {

          snapshot.addNode(node);

        }

        virtual void add(const std::vector<Node>& nodes) {

          for (int i = nodes.size() - 1; i >= 0; ++i) {

            snapshot.addNode(nodes[i]);

          }

        }

        virtual void erase(const Node& node) {

          snapshot.eraseNode(node);

        }

        virtual void erase(const std::vector<Node>& nodes) {

          for (int i = 0; i < int(nodes.size()); ++i) {

            snapshot.eraseNode(nodes[i]);

          }

        }

        virtual void build() {

          Node node;

          std::vector<Node> nodes;

          for (notifier()->first(node); node != INVALID;

               notifier()->next(node)) {

            nodes.push_back(node);

          }

          for (int i = nodes.size() - 1; i >= 0; --i) {

            snapshot.addNode(nodes[i]);

          }

        }

        virtual void clear() {

          Node node;

          for (notifier()->first(node); node != INVALID;

               notifier()->next(node)) {

            snapshot.eraseNode(node);

          }

        }

        Snapshot& snapshot;

      };

      class EdgeObserverProxy : public EdgeNotifier::ObserverBase {

      public:

        EdgeObserverProxy(Snapshot& _snapshot)

          : snapshot(_snapshot) {}

        using EdgeNotifier::ObserverBase::attach;

        using EdgeNotifier::ObserverBase::detach;

        using EdgeNotifier::ObserverBase::attached;

      protected:

        virtual void add(const Edge& edge) {

          snapshot.addEdge(edge);

        }

        virtual void add(const std::vector<Edge>& edges) {

          for (int i = edges.size() - 1; i >= 0; ++i) {

            snapshot.addEdge(edges[i]);

          }

        }

        virtual void erase(const Edge& edge) {

          snapshot.eraseEdge(edge);

        }

        virtual void erase(const std::vector<Edge>& edges) {

          for (int i = 0; i < int(edges.size()); ++i) {

            snapshot.eraseEdge(edges[i]);

          }

        }

        virtual void build() {

          Edge edge;

          std::vector<Edge> edges;

          for (notifier()->first(edge); edge != INVALID;

               notifier()->next(edge)) {

            edges.push_back(edge);

          }

          for (int i = edges.size() - 1; i >= 0; --i) {

            snapshot.addEdge(edges[i]);

          }

        }

        virtual void clear() {

          Edge edge;

          for (notifier()->first(edge); edge != INVALID;

               notifier()->next(edge)) {

            snapshot.eraseEdge(edge);

          }

        }

        Snapshot& snapshot;

      };

      ListGraph *graph;

      NodeObserverProxy node_observer_proxy;

      EdgeObserverProxy edge_observer_proxy;

      std::list<Node> added_nodes;

      std::list<Edge> added_edges;

      void addNode(const Node& node) {

        added_nodes.push_front(node);

      }

      void eraseNode(const Node& node) {

        std::list<Node>::iterator it =

          std::find(added_nodes.begin(), added_nodes.end(), node);

        if (it == added_nodes.end()) {

          clear();

          edge_observer_proxy.detach();

          throw NodeNotifier::ImmediateDetach();

        } else {

          added_nodes.erase(it);

        }

      }

      void addEdge(const Edge& edge) {

        added_edges.push_front(edge);

      }

      void eraseEdge(const Edge& edge) {

        std::list<Edge>::iterator it =

          std::find(added_edges.begin(), added_edges.end(), edge);

        if (it == added_edges.end()) {

          clear();

          node_observer_proxy.detach();

          throw EdgeNotifier::ImmediateDetach();

        } else {

          added_edges.erase(it);

        }

      }

      void attach(ListGraph &_graph) {

        graph = &_graph;

        node_observer_proxy.attach(graph->notifier(Node()));

        edge_observer_proxy.attach(graph->notifier(Edge()));

      }

      void detach() {

        node_observer_proxy.detach();

        edge_observer_proxy.detach();

      }

      bool attached() const {

        return node_observer_proxy.attached();

      }

      void clear() {

        added_nodes.clear();

        added_edges.clear();

      }

    public:

      /// \brief Default constructor.

      ///

      /// Default constructor.

      /// To actually make a snapshot you must call save().

      Snapshot()

        : graph(0), node_observer_proxy(*this),

          edge_observer_proxy(*this) {}