source: lemon-0.x/lemon/smart_graph.h @ 2256:b22dfb6c5ff3

/* -*- C++ -*-
 *
 * This file is a part of LEMON, a generic C++ optimization library
 *
 * Copyright (C) 2003-2006
 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
 * (Egervary Research Group on Combinatorial Optimization, EGRES).
 *
 * Permission to use, modify and distribute this software is granted
 * provided that this copyright notice appears in all copies. For
 * precise terms see the accompanying LICENSE file.
 *
 * This software is provided "AS IS" with no warranty of any kind,
 * express or implied, and with no claim as to its suitability for any
 * purpose.
 *
 */

#ifndef LEMON_SMART_GRAPH_H
#define LEMON_SMART_GRAPH_H

///\ingroup graphs
///\file
///\brief SmartGraph and SmartUGraph classes.

#include <vector>

#include <lemon/bits/invalid.h>

#include <lemon/bits/base_extender.h>
#include <lemon/bits/graph_extender.h>

#include <lemon/bits/utility.h>
#include <lemon/error.h>

#include <lemon/bits/graph_extender.h>

namespace lemon {

  class SmartGraph;
  ///Base of SmartGraph

  ///Base of SmartGraph
  ///
  class SmartGraphBase {
  protected:

    struct NodeT 
    {
      int first_in, first_out;      
      NodeT() {}
    };
    struct EdgeT 
    {
      int target, source, next_in, next_out;      
      EdgeT() {}  
    };

    std::vector<NodeT> nodes;

    std::vector<EdgeT> edges;
    
    
  public:

    typedef SmartGraphBase Graph;

    class Node;
    class Edge;

    
  public:

    SmartGraphBase() : nodes(), edges() { }
    SmartGraphBase(const SmartGraphBase &_g) 
      : nodes(_g.nodes), edges(_g.edges) { }
    
    typedef True NodeNumTag;
    typedef True EdgeNumTag;

    int nodeNum() const { return nodes.size(); }
    int edgeNum() const { return edges.size(); }

    int maxNodeId() const { return nodes.size()-1; }
    int maxEdgeId() const { return edges.size()-1; }

    Node addNode() {
      int n = nodes.size();     
      nodes.push_back(NodeT());
      nodes[n].first_in = -1;
      nodes[n].first_out = -1;
      return Node(n);
    }
    
    Edge addEdge(Node u, Node v) {
      int n = edges.size(); 
      edges.push_back(EdgeT());
      edges[n].source = u.id; 
      edges[n].target = v.id;
      edges[n].next_out = nodes[u.id].first_out;
      edges[n].next_in = nodes[v.id].first_in;
      nodes[u.id].first_out = nodes[v.id].first_in = n;

      return Edge(n);
    }

    void clear() {
      edges.clear();
      nodes.clear();
    }

    Node source(Edge e) const { return Node(edges[e.id].source); }
    Node target(Edge e) const { return Node(edges[e.id].target); }

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

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

    class Node {
      friend class SmartGraphBase;
      friend class SmartGraph;

    protected:
      int id;
      explicit Node(int _id) : id(_id) {}
    public:
      Node() {}
      Node (Invalid) : id(-1) {}
      bool operator==(const Node i) const {return id == i.id;}
      bool operator!=(const Node i) const {return id != i.id;}
      bool operator<(const Node i) const {return id < i.id;}
    };
    

    class Edge {
      friend class SmartGraphBase;
      friend class SmartGraph;

    protected:
      int id;
      explicit Edge(int _id) : id(_id) {}
    public:
      Edge() { }
      Edge (Invalid) : id(-1) {}
      bool operator==(const Edge i) const {return id == i.id;}
      bool operator!=(const Edge i) const {return id != i.id;}
      bool operator<(const Edge i) const {return id < i.id;}
    };

    void first(Node& node) const {
      node.id = nodes.size() - 1;
    }

    static void next(Node& node) {
      --node.id;
    }

    void first(Edge& edge) const {
      edge.id = edges.size() - 1;
    }

    static void next(Edge& edge) {
      --edge.id;
    }

    void firstOut(Edge& edge, const Node& node) const {
      edge.id = nodes[node.id].first_out;
    }

    void nextOut(Edge& edge) const {
      edge.id = edges[edge.id].next_out;
    }

    void firstIn(Edge& edge, const Node& node) const {
      edge.id = nodes[node.id].first_in;
    }
    
    void nextIn(Edge& edge) const {
      edge.id = edges[edge.id].next_in;
    }

  };

  typedef GraphExtender<SmartGraphBase> ExtendedSmartGraphBase;

  /// \ingroup graphs

  ///A smart graph class.

  ///This is a simple and fast graph implementation.
  ///It is also quite memory efficient, but at the price
  ///that <b> it does support only limited (only stack-like)
  ///node and edge deletions</b>.
  ///It conforms to 
  ///the \ref concept::Graph "Graph concept" with an
  ///important extra feature that
  ///its maps are real \ref concept::ReferenceMap "reference map"s.
  ///
  ///\sa concept::Graph.
  ///
  ///\author Alpar Juttner
  class SmartGraph : public ExtendedSmartGraphBase {
  public:

    typedef ExtendedSmartGraphBase Parent;

  private:

    ///SmartGraph is \e not copy constructible. Use GraphCopy() instead.

    ///SmartGraph is \e not copy constructible. Use GraphCopy() instead.
    ///
    SmartGraph(const SmartGraph &) : ExtendedSmartGraphBase() {};
    ///\brief Assignment of SmartGraph to another one is \e not allowed.
    ///Use GraphCopy() instead.

    ///Assignment of SmartGraph to another one is \e not allowed.
    ///Use GraphCopy() instead.
    void operator=(const SmartGraph &) {}

  public:
    
    /// Constructor
    
    /// Constructor.
    ///
    SmartGraph() {};
    
    ///Add a new node to the graph.
    
    /// \return the new node.
    ///
    Node addNode() { return Parent::addNode(); }
    
    ///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); 
    }

    ///Clear the graph.
    
    ///Erase all the nodes and edges from the graph.
    ///
    void clear() {
      Parent::clear();
    }

    ///Split a node.
    
    ///This function splits a node. First a new node is added to the graph,
    ///then the source of each outgoing edge of \c n is moved to this new node.
    ///If \c connect is \c true (this is the default value), then a new edge
    ///from \c n to the newly created node is also added.
    ///\return The newly created node.
    ///
    ///\note The <tt>Edge</tt>s
    ///referencing a moved edge remain
    ///valid. However <tt>InEdge</tt>'s and <tt>OutEdge</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();
      nodes[b.id].first_out=nodes[n.id].first_out;
      nodes[n.id].first_out=-1;
      for(int i=nodes[b.id].first_out;i!=-1;i++) edges[i].source=b.id;
      if(connect) addEdge(n,b);
      return b;
    }

  public:
    
    class Snapshot;

  protected:

    void restoreSnapshot(const Snapshot &s)
    {
      while(s.edge_num<edges.size()) {
        Edge edge = edgeFromId(edges.size()-1);
        Parent::getNotifier(Edge()).erase(edge);
        nodes[edges.back().source].first_out=edges.back().next_out;
        nodes[edges.back().target].first_in=edges.back().next_in;
        edges.pop_back();
      }
      while(s.node_num<nodes.size()) {
        Node node = nodeFromId(nodes.size()-1);
        Parent::getNotifier(Node()).erase(node);
        nodes.pop_back();
      }
    }    

  public:

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

    ///Class to make a snapshot of the graph and to restrore to it later.
    ///
    ///The newly added nodes and edges can be removed using the
    ///restore() function.
    ///\note After you restore a state, you cannot restore
    ///a later state, in other word you cannot add again the edges deleted
    ///by restore() using another one Snapshot instance.
    ///
    ///\warning If you do not use correctly the snapshot that can cause
    ///either broken program, invalid state of the graph, valid but
    ///not the restored graph or no change. Because the runtime performance
    ///the validity of the snapshot is not stored.
    class Snapshot 
    {
      SmartGraph *g;
    protected:
      friend class SmartGraph;
      unsigned int node_num;
      unsigned int edge_num;
    public:
      ///Default constructor.
      
      ///Default constructor.
      ///To actually make a snapshot you must call save().
      ///
      Snapshot() : g(0) {}
      ///Constructor that immediately makes a snapshot
      
      ///This constructor immediately makes a snapshot of the graph.
      ///\param _g The graph we make a snapshot of.
      Snapshot(SmartGraph &_g) :g(&_g) {
        node_num=g->nodes.size();
        edge_num=g->edges.size();
      }

      ///Make a snapshot.

      ///Make a snapshot of the graph.
      ///
      ///This function can be called more than once. In case of a repeated
      ///call, the previous snapshot gets lost.
      ///\param _g The graph we make the snapshot of.
      void save(SmartGraph &_g) 
      {
        g=&_g;
        node_num=g->nodes.size();
        edge_num=g->edges.size();
      }

      ///Undo the changes until a snapshot.
      
      ///Undo the changes until a snapshot created by save().
      ///
      ///\note After you restored a state, you cannot restore
      ///a later state, in other word you cannot add again the edges deleted
      ///by restore().
      void restore()
      {
        g->restoreSnapshot(*this);
      }
    };
  };


  /**************** Undirected List Graph ****************/

  typedef UGraphExtender<UndirGraphExtender<SmartGraphBase> >
  ExtendedSmartUGraphBase;

  /// \ingroup graphs
  ///
  /// \brief A smart undirected graph class.
  ///
  /// This is a simple and fast undirected graph implementation.
  /// It is also quite memory efficient, but at the price
  /// that <b> it does support only limited (only stack-like)
  /// node and edge deletions</b>.
  /// Except from this it conforms to 
  /// the \ref concept::UGraph "UGraph concept".
  ///
  ///It also has an
  ///important extra feature that
  ///its maps are real \ref concept::ReferenceMap "reference map"s.
  ///
  /// \sa concept::UGraph.
  ///
  /// \todo Snapshot hasn't been implemented yet.
  ///
  class SmartUGraph : public ExtendedSmartUGraphBase {
  private:

    ///SmartUGraph is \e not copy constructible. Use UGraphCopy() instead.

    ///SmartUGraph is \e not copy constructible. Use UGraphCopy() instead.
    ///
    SmartUGraph(const SmartUGraph &) : ExtendedSmartUGraphBase() {};

    ///\brief Assignment of SmartUGraph to another one is \e not allowed.
    ///Use UGraphCopy() instead.

    ///Assignment of SmartUGraph to another one is \e not allowed.
    ///Use UGraphCopy() instead.
    void operator=(const SmartUGraph &) {}

  public:

    typedef ExtendedSmartUGraphBase Parent;

    /// Constructor
    
    /// Constructor.
    ///
    SmartUGraph() {}

    ///Add a new node to the graph.
    
    /// \return the new node.
    ///
    Node addNode() { return Parent::addNode(); }
    
    ///Add a new undirected edge to the graph.
    
    ///Add a new undirected edge to the graph with node \c s
    ///and \c t.
    ///\return the new undirected edge.
    UEdge addEdge(const Node& s, const Node& t) { 
      return Parent::addEdge(s, t); 
    }

    ///Clear the graph.
    
    ///Erase all the nodes and edges from the graph.
    ///
    void clear() {
      Parent::clear();
    }

  public:
    
    class Snapshot;

  protected:


    void restoreSnapshot(const Snapshot &s)
    {
      while(s.edge_num<edges.size()) {
        UEdge edge = uEdgeFromId(edges.size()-1);
        Parent::getNotifier(UEdge()).erase(edge);
        std::vector<Edge> dir;
        dir.push_back(Parent::direct(edge, true));
        dir.push_back(Parent::direct(edge, false));
        Parent::getNotifier(Edge()).erase(dir);
        nodes[edges.back().source].first_out=edges.back().next_out;
        nodes[edges.back().target].first_in=edges.back().next_in;
        edges.pop_back();
      }
      while(s.node_num<nodes.size()) {
        Node node = nodeFromId(nodes.size()-1);
        Parent::getNotifier(Node()).erase(node);
        nodes.pop_back();
      }
    }    

  public:

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

    ///Class to make a snapshot of the graph and to restrore to it later.
    ///
    ///The newly added nodes and edges can be removed using the
    ///restore() function.
    ///
    ///\note After you restore a state, you cannot restore
    ///a later state, in other word you cannot add again the edges deleted
    ///by restore() using another one Snapshot instance.
    ///
    ///\warning If you do not use correctly the snapshot that can cause
    ///either broken program, invalid state of the graph, valid but
    ///not the restored graph or no change. Because the runtime performance
    ///the validity of the snapshot is not stored.
    class Snapshot 
    {
      SmartUGraph *g;
    protected:
      friend class SmartUGraph;
      unsigned int node_num;
      unsigned int edge_num;
    public:
      ///Default constructor.
      
      ///Default constructor.
      ///To actually make a snapshot you must call save().
      ///
      Snapshot() : g(0) {}
      ///Constructor that immediately makes a snapshot
      
      ///This constructor immediately makes a snapshot of the graph.
      ///\param _g The graph we make a snapshot of.
      Snapshot(SmartUGraph &_g) :g(&_g) {
        node_num=g->nodes.size();
        edge_num=g->edges.size();
      }

      ///Make a snapshot.

      ///Make a snapshot of the graph.
      ///
      ///This function can be called more than once. In case of a repeated
      ///call, the previous snapshot gets lost.
      ///\param _g The graph we make the snapshot of.
      void save(SmartUGraph &_g) 
      {
        g=&_g;
        node_num=g->nodes.size();
        edge_num=g->edges.size();
      }

      ///Undo the changes until a snapshot.
      
      ///Undo the changes until a snapshot created by save().
      ///
      ///\note After you restored a state, you cannot restore
      ///a later state, in other word you cannot add again the edges deleted
      ///by restore().
      void restore()
      {
        g->restoreSnapshot(*this);
      }
    };
  };


  class SmartBpUGraphBase {
  public:

    class NodeSetError : public LogicError {
    public:
      virtual const char* what() const throw() { 
        return "lemon::SmartBpUGraph::NodeSetError";
      }
    };

  protected:

    struct NodeT {
      int first;
      NodeT() {}
      NodeT(int _first) : first(_first) {}
    };

    struct UEdgeT {
      int aNode, next_out;
      int bNode, next_in;
    };

    std::vector<NodeT> aNodes;
    std::vector<NodeT> bNodes;

    std::vector<UEdgeT> edges;

  public:
  
    class Node {
      friend class SmartBpUGraphBase;
    protected:
      int id;

      explicit Node(int _id) : id(_id) {}
    public:
      Node() {}
      Node(Invalid) : id(-1) {}
      bool operator==(const Node i) const {return id==i.id;}
      bool operator!=(const Node i) const {return id!=i.id;}
      bool operator<(const Node i) const {return id<i.id;}
    };

    class UEdge {
      friend class SmartBpUGraphBase;
    protected:
      int id;

      UEdge(int _id) : id(_id) {}
    public:
      UEdge() {}
      UEdge(Invalid) : id(-1) {}
      bool operator==(const UEdge i) const {return id==i.id;}
      bool operator!=(const UEdge i) const {return id!=i.id;}
      bool operator<(const UEdge i) const {return id<i.id;}
    };

    void firstANode(Node& node) const {
      node.id = 2 * aNodes.size() - 2;
      if (node.id < 0) node.id = -1; 
    }
    void nextANode(Node& node) const {
      node.id -= 2;
      if (node.id < 0) node.id = -1; 
    }

    void firstBNode(Node& node) const {
      node.id = 2 * bNodes.size() - 1;
    }
    void nextBNode(Node& node) const {
      node.id -= 2;
    }

    void first(Node& node) const {
      if (aNodes.size() > 0) {
        node.id = 2 * aNodes.size() - 2;
      } else {
        node.id = 2 * bNodes.size() - 1;
      }
    }
    void next(Node& node) const {
      node.id -= 2;
      if (node.id == -2) {
        node.id = 2 * bNodes.size() - 1;
      }
    }
  
    void first(UEdge& edge) const {
      edge.id = edges.size() - 1;
    }
    void next(UEdge& edge) const {
      --edge.id;
    }

    void firstFromANode(UEdge& edge, const Node& node) const {
      LEMON_ASSERT((node.id & 1) == 0, NodeSetError());
      edge.id = aNodes[node.id >> 1].first;
    }
    void nextFromANode(UEdge& edge) const {
      edge.id = edges[edge.id].next_out;
    }

    void firstFromBNode(UEdge& edge, const Node& node) const {
      LEMON_ASSERT((node.id & 1) == 1, NodeSetError());
      edge.id = bNodes[node.id >> 1].first;
    }
    void nextFromBNode(UEdge& edge) const {
      edge.id = edges[edge.id].next_in;
    }

    static int id(const Node& node) {
      return node.id;
    }
    static Node nodeFromId(int id) {
      return Node(id);
    }
    int maxNodeId() const {
      return aNodes.size() > bNodes.size() ?
        aNodes.size() * 2 - 2 : bNodes.size() * 2 - 1;
    }
  
    static int id(const UEdge& edge) {
      return edge.id;
    }
    static UEdge uEdgeFromId(int id) {
      return UEdge(id);
    }
    int maxUEdgeId() const {
      return edges.size();
    }
  
    static int aNodeId(const Node& node) {
      return node.id >> 1;
    }
    static Node nodeFromANodeId(int id) {
      return Node(id << 1);
    }
    int maxANodeId() const {
      return aNodes.size();
    }

    static int bNodeId(const Node& node) {
      return node.id >> 1;
    }
    static Node nodeFromBNodeId(int id) {
      return Node((id << 1) + 1);
    }
    int maxBNodeId() const {
      return bNodes.size();
    }

    Node aNode(const UEdge& edge) const {
      return Node(edges[edge.id].aNode);
    }
    Node bNode(const UEdge& edge) const {
      return Node(edges[edge.id].bNode);
    }

    static bool aNode(const Node& node) {
      return (node.id & 1) == 0;
    }

    static bool bNode(const Node& node) {
      return (node.id & 1) == 1;
    }

    Node addANode() {
      NodeT nodeT;
      nodeT.first = -1;
      aNodes.push_back(nodeT);
      return Node(aNodes.size() * 2 - 2);
    }

    Node addBNode() {
      NodeT nodeT;
      nodeT.first = -1;
      bNodes.push_back(nodeT);
      return Node(bNodes.size() * 2 - 1);
    }

    UEdge addEdge(const Node& source, const Node& target) {
      LEMON_ASSERT(((source.id ^ target.id) & 1) == 1, NodeSetError());
      UEdgeT edgeT;
      if ((source.id & 1) == 0) {
        edgeT.aNode = source.id;
        edgeT.bNode = target.id;
      } else {
        edgeT.aNode = target.id;
        edgeT.bNode = source.id;
      }
      edgeT.next_out = aNodes[edgeT.aNode >> 1].first;
      aNodes[edgeT.aNode >> 1].first = edges.size();
      edgeT.next_in = bNodes[edgeT.bNode >> 1].first;
      bNodes[edgeT.bNode >> 1].first = edges.size();
      edges.push_back(edgeT);
      return UEdge(edges.size() - 1);
    }

    void clear() {
      aNodes.clear();
      bNodes.clear();
      edges.clear();
    }

    typedef True NodeNumTag;
    int nodeNum() const { return aNodes.size() + bNodes.size(); }
    int aNodeNum() const { return aNodes.size(); }
    int bNodeNum() const { return bNodes.size(); }

    typedef True EdgeNumTag;
    int uEdgeNum() const { return edges.size(); }

  };


  typedef BpUGraphExtender<BidirBpUGraphExtender<SmartBpUGraphBase> >
  ExtendedSmartBpUGraphBase;

  /// \ingroup graphs
  ///
  /// \brief A smart bipartite undirected graph class.
  ///
  /// This is a simple and fast bipartite undirected graph implementation.
  /// It is also quite memory efficient, but at the price
  /// that <b> it does not support node and edge deletions</b>.
  /// Except from this it conforms to 
  /// the \ref concept::BpUGraph "BpUGraph concept".
  ///
  ///It also has an
  ///important extra feature that
  ///its maps are real \ref concept::ReferenceMap "reference map"s.
  ///
  /// \sa concept::BpUGraph.
  ///
  class SmartBpUGraph : public ExtendedSmartBpUGraphBase {
  private:

    /// \brief SmartBpUGraph is \e not copy constructible.
    ///
    ///SmartBpUGraph is \e not copy constructible.
    SmartBpUGraph(const SmartBpUGraph &) : ExtendedSmartBpUGraphBase() {};

    /// \brief Assignment of SmartBpUGraph to another one is \e not
    /// allowed.
    ///
    /// Assignment of SmartBpUGraph to another one is \e not allowed.
    void operator=(const SmartBpUGraph &) {}

  public:

    typedef ExtendedSmartBpUGraphBase Parent;

    ///Constructor
    
    ///Constructor.
    ///
    SmartBpUGraph() : ExtendedSmartBpUGraphBase() {}

    ///Add a new ANode to the graph.
    
    /// \return the new node.
    ///
    Node addANode() { return Parent::addANode(); }

    ///Add a new BNode to the graph.
    
    /// \return the new node.
    ///
    Node addBNode() { return Parent::addBNode(); }
    
    ///Add a new undirected edge to the graph.
    
    ///Add a new undirected edge to the graph with node \c s
    ///and \c t.
    ///\return the new undirected edge.
    UEdge addEdge(const Node& s, const Node& t) { 
      return Parent::addEdge(s, t); 
    }

    ///Clear the graph.
    
    ///Erase all the nodes and edges from the graph.
    ///
    void clear() {
      Parent::clear();
    }
    
  public:

    class Snapshot;

  protected:
    
    void restoreSnapshot(const Snapshot &s)
    {
      while(s.edge_num<edges.size()) {
        UEdge edge = uEdgeFromId(edges.size()-1);
        Parent::getNotifier(UEdge()).erase(edge);
        std::vector<Edge> dir;
        dir.push_back(Parent::direct(edge, true));
        dir.push_back(Parent::direct(edge, false));
        Parent::getNotifier(Edge()).erase(dir);
        aNodes[edges.back().aNode >> 1].first=edges.back().next_out;
        bNodes[edges.back().bNode >> 1].first=edges.back().next_in;
        edges.pop_back();
      }
      while(s.anode_num<aNodes.size()) {
        Node node = nodeFromANodeId(aNodes.size() - 1);
        Parent::getNotifier(ANode()).erase(node);
        Parent::getNotifier(Node()).erase(node);
        aNodes.pop_back();
      }
      while(s.bnode_num<bNodes.size()) {
        Node node = nodeFromBNodeId(bNodes.size() - 1);
        Parent::getNotifier(BNode()).erase(node);
        Parent::getNotifier(Node()).erase(node);
        bNodes.pop_back();
      }
    }    

  public:

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

    ///Class to make a snapshot of the graph and to restrore to it later.
    ///
    ///The newly added nodes and edges can be removed using the
    ///restore() function.
    ///
    ///\note After you restore a state, you cannot restore
    ///a later state, in other word you cannot add again the edges deleted
    ///by restore() using another one Snapshot instance.
    ///
    ///\warning If you do not use correctly the snapshot that can cause
    ///either broken program, invalid state of the graph, valid but
    ///not the restored graph or no change. Because the runtime performance
    ///the validity of the snapshot is not stored.
    class Snapshot 
    {
      SmartBpUGraph *g;
    protected:
      friend class SmartBpUGraph;
      unsigned int anode_num;
      unsigned int bnode_num;
      unsigned int edge_num;
    public:
      ///Default constructor.
      
      ///Default constructor.
      ///To actually make a snapshot you must call save().
      ///
      Snapshot() : g(0) {}

      ///Constructor that immediately makes a snapshot
      
      ///This constructor immediately makes a snapshot of the graph.
      ///\param _g The graph we make a snapshot of.
      Snapshot(SmartBpUGraph &_g) : g(&_g) {
        anode_num=g->aNodes.size();
        bnode_num=g->bNodes.size();
        edge_num=g->edges.size();
      }

      ///Make a snapshot.

      ///Make a snapshot of the graph.
      ///
      ///This function can be called more than once. In case of a repeated
      ///call, the previous snapshot gets lost.
      ///\param _g The graph we make the snapshot of.
      void save(SmartBpUGraph &_g) 
      {
        g=&_g;
        anode_num=g->aNodes.size();
        bnode_num=g->bNodes.size();
        edge_num=g->edges.size();
      }

      ///Undo the changes until a snapshot.
      
      ///Undo the changes until a snapshot created by save().
      ///
      ///\note After you restored a state, you cannot restore
      ///a later state, in other word you cannot add again the edges deleted
      ///by restore().
      void restore()
      {
        g->restoreSnapshot(*this);
      }
    };
  };

  
  /// @}  
} //namespace lemon


#endif //LEMON_SMART_GRAPH_H