protected:

   protected:

     void saveSnapshot(Snapshot &s)

     void saveSnapshot(Snapshot &s)

     {

     {

       s.node_num = nodes.size();

       s.node_num = nodes.size();

       s.edge_num = edges.size();

       s.edge_num = edges.size();

     }

     }

     void restoreSnapshot(const Snapshot &s)

     void restoreSnapshot(const Snapshot &s)

     ///either broken program, invalid state of the graph, valid but

     ///either broken program, invalid state of the graph, valid but

     ///not the restored graph or no change. Because the runtime performance

     ///not the restored graph or no change. Because the runtime performance

     ///the validity of the snapshot is not stored.

     ///the validity of the snapshot is not stored.

     class Snapshot 

     class Snapshot 

     {

     {

     protected:

     protected:

       friend class SmartUGraph;

       friend class SmartUGraph;

       unsigned int node_num;

       unsigned int node_num;

       unsigned int edge_num;

       unsigned int edge_num;

     public:

     public:

       ///Default constructor.

       ///Default constructor.

       ///Default constructor.

       ///Default constructor.

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

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

       ///

       ///

       ///Constructor that immediately makes a snapshot

       ///Constructor that immediately makes a snapshot

       ///This constructor immediately makes a snapshot of the graph.

       ///This constructor immediately makes a snapshot of the graph.

       ///\param g The graph we make a snapshot of.

       ///\param g The graph we make a snapshot of.

       Snapshot(SmartUGraph &g) {

       Snapshot(SmartUGraph &g) {

       ///\note After you restored a state, you cannot restore

       ///\note After you restored a state, you cannot restore

       ///a later state, in other word you cannot add again the edges deleted

       ///a later state, in other word you cannot add again the edges deleted

       ///by restore().

       ///by restore().

       void restore()

       void restore()

       {

       {

       }

       }

     };

     };

   };

   };