/* -*- C++ -*-

 *

 * This file is a part of LEMON, a generic C++ optimization library

 *

 * Copyright (C) 2003-2007

 * 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

  ///

  ///\brief 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 concepts::Graph "Graph concept" with an

  ///important extra feature that

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

  ///

  ///\sa concepts::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); 

    }

    /// \brief Using this it is possible to avoid the superfluous memory

    /// allocation.

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

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

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

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

    /// to build the graph.

    /// \sa reserveEdge

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

    /// \brief Using this it is possible to avoid the superfluous memory

    /// allocation.

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

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

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

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

    /// to build the graph.

    /// \sa reserveNode

    void reserveEdge(int m) { edges.reserve(m); };

    ///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::notifier(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::notifier(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);

      }

    };

  };

  class SmartUGraphBase {

  protected:

    struct NodeT {

      int first_out;

    };

    struct EdgeT {

      int target;

      int next_out;

    };

    std::vector<NodeT> nodes;

    std::vector<EdgeT> edges;

    int first_free_edge;

  public:

    typedef SmartUGraphBase Graph;

    class Node;

    class Edge;

    class UEdge;

    class Node {

      friend class SmartUGraphBase;

    protected:

      int id;

      explicit Node(int pid) { id = pid;}

    public:

      Node() {}

      Node (Invalid) { id = -1; }

      bool operator==(const Node& node) const {return id == node.id;}

      bool operator!=(const Node& node) const {return id != node.id;}

      bool operator<(const Node& node) const {return id < node.id;}

    };

    class UEdge {

      friend class SmartUGraphBase;

    protected:

      int id;

      explicit UEdge(int pid) { id = pid;}

    public:

      UEdge() {}

      UEdge (Invalid) { id = -1; }

      bool operator==(const UEdge& edge) const {return id == edge.id;}

      bool operator!=(const UEdge& edge) const {return id != edge.id;}

      bool operator<(const UEdge& edge) const {return id < edge.id;}

    };

    class Edge {

      friend class SmartUGraphBase;

    protected:

      int id;

      explicit Edge(int pid) { id = pid;}

    public:

      operator UEdge() const { return uEdgeFromId(id / 2); }

      Edge() {}

      Edge (Invalid) { id = -1; }

      bool operator==(const Edge& edge) const {return id == edge.id;}

      bool operator!=(const Edge& edge) const {return id != edge.id;}

      bool operator<(const Edge& edge) const {return id < edge.id;}

    };

    SmartUGraphBase()

      : nodes(), edges() {}

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

    int maxUEdgeId() const { return edges.size() / 2 - 1; }

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

    Node source(Edge e) const { return Node(edges[e.id ^ 1].target); }

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

    Node source(UEdge e) const { return Node(edges[2 * e.id].target); }

    Node target(UEdge e) const { return Node(edges[2 * e.id + 1].target); }

    static bool direction(Edge e) {

      return (e.id & 1) == 1;

    }

    static Edge direct(UEdge e, bool d) {

      return Edge(e.id * 2 + (d ? 1 : 0));

    }

    void first(Node& node) const { 

      node.id = nodes.size() - 1;

    }

    void next(Node& node) const {

      --node.id;

    }

    void first(Edge& edge) const { 

      edge.id = edges.size() - 1;

    }

    void next(Edge& edge) const {

      --edge.id;

    }

    void first(UEdge& edge) const { 

      edge.id = edges.size() / 2 - 1;

    }

    void next(UEdge& edge) const {

      --edge.id;

    }

    void firstOut(Edge &edge, const Node& v) const {

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

    }

    void nextOut(Edge &edge) const {

      edge.id = edges[edge.id].next_out;

    }

    void firstIn(Edge &edge, const Node& v) const {

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

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

    }

    void nextIn(Edge &edge) const {

      edge.id = ((edges[edge.id ^ 1].next_out) ^ 1);

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

    }

    void firstInc(UEdge &edge, bool& d, const Node& v) const {

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

      if (de != -1) {

        edge.id = de / 2;

        d = ((de & 1) == 1);

      } else {

        edge.id = -1;

        d = true;

      }

    }

    void nextInc(UEdge &edge, bool& d) const {

      int de = (edges[(edge.id * 2) | (d ? 1 : 0)].next_out);

      if (de != -1) {

        edge.id = de / 2;

        d = ((de & 1) == 1);

      } else {

        edge.id = -1;

        d = true;      

      }

    }

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

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

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

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

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

    static UEdge uEdgeFromId(int id) { return UEdge(id);}

    Node addNode() {     

      int n = nodes.size();

      nodes.push_back(NodeT());

      nodes[n].first_out = -1;

      return Node(n);

    }

    UEdge addEdge(Node u, Node v) {

      int n = edges.size();

      edges.push_back(EdgeT());

      edges.push_back(EdgeT());

      edges[n].target = u.id;

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

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

      nodes[v.id].first_out = n;

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

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

      return UEdge(n / 2);

    }

    void clear() {

      edges.clear();

      nodes.clear();

    }

  };

  typedef UGraphExtender<SmartUGraphBase> 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 concepts::UGraph "UGraph concept".

  ///

  ///It also has an

  ///important extra feature that

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

  ///

  /// \sa concepts::UGraph.

  ///

  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;

    typedef Parent::OutEdgeIt IncEdgeIt;

    /// 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 saveSnapshot(Snapshot &s)

    {

      s.graph = this;

      s.node_num = nodes.size();

      s.edge_num = edges.size();

    }

    void restoreSnapshot(const Snapshot &s)

    {

      while(s.edge_num<edges.size()) {

        int n=edges.size()-1;

        UEdge edge=uEdgeFromId(n/2);

	Parent::notifier(UEdge()).erase(edge);

        std::vector<Edge> dir;

        dir.push_back(edgeFromId(n));

        dir.push_back(edgeFromId(n-1));

	Parent::notifier(Edge()).erase(dir);

	nodes[edges[n].target].first_out=edges[n].next_out;

	nodes[edges[n-1].target].first_out=edges[n-1].next_out;

	edges.pop_back();

	edges.pop_back();

      }

      while(s.node_num<nodes.size()) {

        int n=nodes.size()-1;

        Node node = nodeFromId(n);

	Parent::notifier(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 *graph;

    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() : graph(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.saveSnapshot(*this);

      }

      ///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.saveSnapshot(*this);

      }

      ///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()

      {

        graph->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 concepts::BpUGraph "BpUGraph concept".

  ///

  ///It also has an

  ///important extra feature that

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

  ///

  /// \sa concepts::BpUGraph.