/* -*- mode: C++; indent-tabs-mode: nil; -*-

 *

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

 *

 * Copyright (C) 2003-2008

 * 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_TOPOLOGY_H

#define LEMON_TOPOLOGY_H

#include <lemon/dfs.h>

#include <lemon/bfs.h>

#include <lemon/core.h>

#include <lemon/maps.h>

#include <lemon/adaptors.h>

#include <lemon/concepts/digraph.h>

#include <lemon/concepts/graph.h>

#include <lemon/concept_check.h>

#include <stack>

#include <functional>

/// \ingroup connectivity

/// \file

/// \brief Connectivity algorithms

///

/// Connectivity algorithms

namespace lemon {

  /// \ingroup connectivity

  ///

  /// \brief Check whether the given undirected graph is connected.

  ///

  /// Check whether the given undirected graph is connected.

  /// \param graph The undirected graph.

  /// \return %True when there is path between any two nodes in the graph.

  /// \note By definition, the empty graph is connected.

  template <typename Graph>

  bool connected(const Graph& graph) {

    checkConcept<concepts::Graph, Graph>();

    typedef typename Graph::NodeIt NodeIt;

    if (NodeIt(graph) == INVALID) return true;

    Dfs<Graph> dfs(graph);

    dfs.run(NodeIt(graph));

    for (NodeIt it(graph); it != INVALID; ++it) {

      if (!dfs.reached(it)) {

        return false;

      }

    }

    return true;

  }

  /// \ingroup connectivity

  ///

  /// \brief Count the number of connected components of an undirected graph

  ///

  /// Count the number of connected components of an undirected graph

  ///

  /// \param graph The graph. It must be undirected.

  /// \return The number of components

  /// \note By definition, the empty graph consists

  /// of zero connected components.

  template <typename Graph>

  int countConnectedComponents(const Graph &graph) {

    checkConcept<concepts::Graph, Graph>();

    typedef typename Graph::Node Node;

    typedef typename Graph::Arc Arc;

    typedef NullMap<Node, Arc> PredMap;

    typedef NullMap<Node, int> DistMap;

    int compNum = 0;

    typename Bfs<Graph>::

      template SetPredMap<PredMap>::

      template SetDistMap<DistMap>::

      Create bfs(graph);

    PredMap predMap;

    bfs.predMap(predMap);

    DistMap distMap;

    bfs.distMap(distMap);

    bfs.init();

    for(typename Graph::NodeIt n(graph); n != INVALID; ++n) {

      if (!bfs.reached(n)) {

        bfs.addSource(n);

        bfs.start();

        ++compNum;

      }

    }

    return compNum;

  }

  /// \ingroup connectivity

  ///

  /// \brief Find the connected components of an undirected graph

  ///

  /// Find the connected components of an undirected graph.

  ///

  /// \param graph The graph. It must be undirected.

  /// \retval compMap A writable node map. The values will be set from 0 to

  /// the number of the connected components minus one. Each values of the map

  /// will be set exactly once, the values of a certain component will be

  /// set continuously.

  /// \return The number of components

  ///

  template <class Graph, class NodeMap>

  int connectedComponents(const Graph &graph, NodeMap &compMap) {

    checkConcept<concepts::Graph, Graph>();

    typedef typename Graph::Node Node;

    typedef typename Graph::Arc Arc;

    checkConcept<concepts::WriteMap<Node, int>, NodeMap>();

    typedef NullMap<Node, Arc> PredMap;

    typedef NullMap<Node, int> DistMap;

    int compNum = 0;

    typename Bfs<Graph>::

      template SetPredMap<PredMap>::

      template SetDistMap<DistMap>::

      Create bfs(graph);

    PredMap predMap;

    bfs.predMap(predMap);

    DistMap distMap;

    bfs.distMap(distMap);

    bfs.init();

    for(typename Graph::NodeIt n(graph); n != INVALID; ++n) {

      if(!bfs.reached(n)) {

        bfs.addSource(n);

        while (!bfs.emptyQueue()) {

          compMap.set(bfs.nextNode(), compNum);

          bfs.processNextNode();

        }

        ++compNum;

      }

    }

    return compNum;

  }

  namespace _topology_bits {

    template <typename Digraph, typename Iterator >

    struct LeaveOrderVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      LeaveOrderVisitor(Iterator it) : _it(it) {}

      void leave(const Node& node) {

        *(_it++) = node;

      }

    private:

      Iterator _it;

    };

    template <typename Digraph, typename Map>

    struct FillMapVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      typedef typename Map::Value Value;

      FillMapVisitor(Map& map, Value& value)

        : _map(map), _value(value) {}

      void reach(const Node& node) {

        _map.set(node, _value);

      }

    private:

      Map& _map;

      Value& _value;

    };

    template <typename Digraph, typename ArcMap>

    struct StronglyConnectedCutEdgesVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      typedef typename Digraph::Arc Arc;

      StronglyConnectedCutEdgesVisitor(const Digraph& digraph,

                                       ArcMap& cutMap,

                                       int& cutNum)

        : _digraph(digraph), _cutMap(cutMap), _cutNum(cutNum),

          _compMap(digraph), _num(0) {

      }

      void stop(const Node&) {

        ++_num;

      }

      void reach(const Node& node) {

        _compMap.set(node, _num);

      }

      void examine(const Arc& arc) {

         if (_compMap[_digraph.source(arc)] !=

             _compMap[_digraph.target(arc)]) {

           _cutMap.set(arc, true);

           ++_cutNum;

         }

      }

    private:

      const Digraph& _digraph;

      ArcMap& _cutMap;

      int& _cutNum;

      typename Digraph::template NodeMap<int> _compMap;

      int _num;

    };

  }

  /// \ingroup connectivity

  ///

  /// \brief Check whether the given directed graph is strongly connected.

  ///

  /// Check whether the given directed graph is strongly connected. The

  /// graph is strongly connected when any two nodes of the graph are

  /// connected with directed paths in both direction.

  /// \return %False when the graph is not strongly connected.

  /// \see connected

  ///

  /// \note By definition, the empty graph is strongly connected.

  template <typename Digraph>

  bool stronglyConnected(const Digraph& digraph) {

    checkConcept<concepts::Digraph, Digraph>();

    typedef typename Digraph::Node Node;

    typedef typename Digraph::NodeIt NodeIt;

    typename Digraph::Node source = NodeIt(digraph);

    if (source == INVALID) return true;

    using namespace _topology_bits;

    typedef DfsVisitor<Digraph> Visitor;

    Visitor visitor;

    DfsVisit<Digraph, Visitor> dfs(digraph, visitor);

    dfs.init();

    dfs.addSource(source);

    dfs.start();

    for (NodeIt it(digraph); it != INVALID; ++it) {

      if (!dfs.reached(it)) {

        return false;

      }

    }

    typedef ReverseDigraph<const Digraph> RDigraph;

    RDigraph rdigraph(digraph);

    typedef DfsVisitor<Digraph> RVisitor;

    RVisitor rvisitor;

    DfsVisit<RDigraph, RVisitor> rdfs(rdigraph, rvisitor);

    rdfs.init();

    rdfs.addSource(source);

    rdfs.start();

    for (NodeIt it(rdigraph); it != INVALID; ++it) {

      if (!rdfs.reached(it)) {

        return false;

      }

    }

    return true;

  }

  /// \ingroup connectivity

  ///

  /// \brief Count the strongly connected components of a directed graph

  ///

  /// Count the strongly connected components of a directed graph.

  /// The strongly connected components are the classes of an

  /// equivalence relation on the nodes of the graph. Two nodes are in

  /// the same class if they are connected with directed paths in both

  /// direction.

  ///

  /// \param graph The graph.

  /// \return The number of components

  /// \note By definition, the empty graph has zero

  /// strongly connected components.

  template <typename Digraph>

  int countStronglyConnectedComponents(const Digraph& digraph) {

    checkConcept<concepts::Digraph, Digraph>();

    using namespace _topology_bits;

    typedef typename Digraph::Node Node;

    typedef typename Digraph::Arc Arc;

    typedef typename Digraph::NodeIt NodeIt;

    typedef typename Digraph::ArcIt ArcIt;

    typedef std::vector<Node> Container;

    typedef typename Container::iterator Iterator;

    Container nodes(countNodes(digraph));

    typedef LeaveOrderVisitor<Digraph, Iterator> Visitor;

    Visitor visitor(nodes.begin());

    DfsVisit<Digraph, Visitor> dfs(digraph, visitor);

    dfs.init();

    for (NodeIt it(digraph); it != INVALID; ++it) {

      if (!dfs.reached(it)) {

        dfs.addSource(it);

        dfs.start();

      }

    }

    typedef typename Container::reverse_iterator RIterator;

    typedef ReverseDigraph<const Digraph> RDigraph;

    RDigraph rdigraph(digraph);

    typedef DfsVisitor<Digraph> RVisitor;

    RVisitor rvisitor;

    DfsVisit<RDigraph, RVisitor> rdfs(rdigraph, rvisitor);

    int compNum = 0;

    rdfs.init();

    for (RIterator it = nodes.rbegin(); it != nodes.rend(); ++it) {

      if (!rdfs.reached(*it)) {

        rdfs.addSource(*it);

        rdfs.start();

        ++compNum;

      }

    }

    return compNum;

  }

  /// \ingroup connectivity

  ///

  /// \brief Find the strongly connected components of a directed graph

  ///

  /// Find the strongly connected components of a directed graph.  The

  /// strongly connected components are the classes of an equivalence

  /// relation on the nodes of the graph. Two nodes are in

  /// relationship when there are directed paths between them in both

  /// direction. In addition, the numbering of components will satisfy

  /// that there is no arc going from a higher numbered component to

  /// a lower.

  ///

  /// \param digraph The digraph.

  /// \retval compMap A writable node map. The values will be set from 0 to

  /// the number of the strongly connected components minus one. Each value

  /// of the map will be set exactly once, the values of a certain component

  /// will be set continuously.

  /// \return The number of components

  ///

  template <typename Digraph, typename NodeMap>

  int stronglyConnectedComponents(const Digraph& digraph, NodeMap& compMap) {

    checkConcept<concepts::Digraph, Digraph>();

    typedef typename Digraph::Node Node;

    typedef typename Digraph::NodeIt NodeIt;

    checkConcept<concepts::WriteMap<Node, int>, NodeMap>();

    using namespace _topology_bits;

    typedef std::vector<Node> Container;

    typedef typename Container::iterator Iterator;

    Container nodes(countNodes(digraph));

    typedef LeaveOrderVisitor<Digraph, Iterator> Visitor;

    Visitor visitor(nodes.begin());

    DfsVisit<Digraph, Visitor> dfs(digraph, visitor);

    dfs.init();

    for (NodeIt it(digraph); it != INVALID; ++it) {

      if (!dfs.reached(it)) {

        dfs.addSource(it);

        dfs.start();

      }

    }

    typedef typename Container::reverse_iterator RIterator;

    typedef ReverseDigraph<const Digraph> RDigraph;

    RDigraph rdigraph(digraph);

    int compNum = 0;

    typedef FillMapVisitor<RDigraph, NodeMap> RVisitor;

    RVisitor rvisitor(compMap, compNum);

    DfsVisit<RDigraph, RVisitor> rdfs(rdigraph, rvisitor);

    rdfs.init();

    for (RIterator it = nodes.rbegin(); it != nodes.rend(); ++it) {

      if (!rdfs.reached(*it)) {

        rdfs.addSource(*it);

        rdfs.start();

        ++compNum;

      }

    }

    return compNum;

  }

  /// \ingroup connectivity

  ///

  /// \brief Find the cut arcs of the strongly connected components.

  ///

  /// Find the cut arcs of the strongly connected components.

  /// The strongly connected components are the classes of an equivalence

  /// relation on the nodes of the graph. Two nodes are in relationship

  /// when there are directed paths between them in both direction.

  /// The strongly connected components are separated by the cut arcs.

  ///

  /// \param graph The graph.

  /// \retval cutMap A writable node map. The values will be set true when the

  /// arc is a cut arc.

  ///

  /// \return The number of cut arcs

  template <typename Digraph, typename ArcMap>

  int stronglyConnectedCutArcs(const Digraph& graph, ArcMap& cutMap) {

    checkConcept<concepts::Digraph, Digraph>();

    typedef typename Digraph::Node Node;

    typedef typename Digraph::Arc Arc;

    typedef typename Digraph::NodeIt NodeIt;

    checkConcept<concepts::WriteMap<Arc, bool>, ArcMap>();

    using namespace _topology_bits;

    typedef std::vector<Node> Container;

    typedef typename Container::iterator Iterator;

    Container nodes(countNodes(graph));

    typedef LeaveOrderVisitor<Digraph, Iterator> Visitor;

    Visitor visitor(nodes.begin());

    DfsVisit<Digraph, Visitor> dfs(graph, visitor);

    dfs.init();

    for (NodeIt it(graph); it != INVALID; ++it) {

      if (!dfs.reached(it)) {

        dfs.addSource(it);

        dfs.start();

      }

    }

    typedef typename Container::reverse_iterator RIterator;

    typedef ReverseDigraph<const Digraph> RDigraph;

    RDigraph rgraph(graph);

    int cutNum = 0;

    typedef StronglyConnectedCutEdgesVisitor<RDigraph, ArcMap> RVisitor;

    RVisitor rvisitor(rgraph, cutMap, cutNum);

    DfsVisit<RDigraph, RVisitor> rdfs(rgraph, rvisitor);

    rdfs.init();

    for (RIterator it = nodes.rbegin(); it != nodes.rend(); ++it) {

      if (!rdfs.reached(*it)) {

        rdfs.addSource(*it);

        rdfs.start();

      }

    }

    return cutNum;

  }

  namespace _topology_bits {

    template <typename Digraph>

    class CountBiNodeConnectedComponentsVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      typedef typename Digraph::Arc Arc;

      typedef typename Digraph::Edge Edge;

      CountBiNodeConnectedComponentsVisitor(const Digraph& graph, int &compNum)

        : _graph(graph), _compNum(compNum),

          _numMap(graph), _retMap(graph), _predMap(graph), _num(0) {}

      void start(const Node& node) {

        _predMap.set(node, INVALID);

      }

      void reach(const Node& node) {

        _numMap.set(node, _num);

        _retMap.set(node, _num);

        ++_num;

      }

      void discover(const Arc& edge) {

        _predMap.set(_graph.target(edge), _graph.source(edge));

      }

      void examine(const Arc& edge) {

        if (_graph.source(edge) == _graph.target(edge) &&

            _graph.direction(edge)) {

          ++_compNum;

          return;

        }

        if (_predMap[_graph.source(edge)] == _graph.target(edge)) {

          return;

        }

        if (_retMap[_graph.source(edge)] > _numMap[_graph.target(edge)]) {

          _retMap.set(_graph.source(edge), _numMap[_graph.target(edge)]);

        }

      }

      void backtrack(const Arc& edge) {

        if (_retMap[_graph.source(edge)] > _retMap[_graph.target(edge)]) {

          _retMap.set(_graph.source(edge), _retMap[_graph.target(edge)]);

        }

        if (_numMap[_graph.source(edge)] <= _retMap[_graph.target(edge)]) {

          ++_compNum;

        }

      }

    private:

      const Digraph& _graph;

      int& _compNum;

      typename Digraph::template NodeMap<int> _numMap;

      typename Digraph::template NodeMap<int> _retMap;

      typename Digraph::template NodeMap<Node> _predMap;

      int _num;

    };

    template <typename Digraph, typename ArcMap>

    class BiNodeConnectedComponentsVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      typedef typename Digraph::Arc Arc;

      typedef typename Digraph::Edge Edge;

      BiNodeConnectedComponentsVisitor(const Digraph& graph,

                                       ArcMap& compMap, int &compNum)

        : _graph(graph), _compMap(compMap), _compNum(compNum),

          _numMap(graph), _retMap(graph), _predMap(graph), _num(0) {}

      void start(const Node& node) {

        _predMap.set(node, INVALID);

      }

      void reach(const Node& node) {

        _numMap.set(node, _num);

        _retMap.set(node, _num);

        ++_num;

      }

      void discover(const Arc& edge) {

        Node target = _graph.target(edge);

        _predMap.set(target, edge);

        _edgeStack.push(edge);

      }

      void examine(const Arc& edge) {

        Node source = _graph.source(edge);

        Node target = _graph.target(edge);

        if (source == target && _graph.direction(edge)) {

          _compMap.set(edge, _compNum);

          ++_compNum;

          return;

        }

        if (_numMap[target] < _numMap[source]) {

          if (_predMap[source] != _graph.oppositeArc(edge)) {

            _edgeStack.push(edge);

          }

        }

        if (_predMap[source] != INVALID &&

            target == _graph.source(_predMap[source])) {

          return;

        }

        if (_retMap[source] > _numMap[target]) {

          _retMap.set(source, _numMap[target]);

        }

      }

      void backtrack(const Arc& edge) {

        Node source = _graph.source(edge);

        Node target = _graph.target(edge);

        if (_retMap[source] > _retMap[target]) {

          _retMap.set(source, _retMap[target]);

        }

        if (_numMap[source] <= _retMap[target]) {

          while (_edgeStack.top() != edge) {

            _compMap.set(_edgeStack.top(), _compNum);

            _edgeStack.pop();

          }

          _compMap.set(edge, _compNum);

          _edgeStack.pop();

          ++_compNum;

        }

      }

    private:

      const Digraph& _graph;

      ArcMap& _compMap;

      int& _compNum;

      typename Digraph::template NodeMap<int> _numMap;

      typename Digraph::template NodeMap<int> _retMap;

      typename Digraph::template NodeMap<Arc> _predMap;

      std::stack<Edge> _edgeStack;

      int _num;

    };

    template <typename Digraph, typename NodeMap>

    class BiNodeConnectedCutNodesVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      typedef typename Digraph::Arc Arc;

      typedef typename Digraph::Edge Edge;

      BiNodeConnectedCutNodesVisitor(const Digraph& graph, NodeMap& cutMap,

                                     int& cutNum)

        : _graph(graph), _cutMap(cutMap), _cutNum(cutNum),

          _numMap(graph), _retMap(graph), _predMap(graph), _num(0) {}

      void start(const Node& node) {

        _predMap.set(node, INVALID);

        rootCut = false;

      }

      void reach(const Node& node) {

        _numMap.set(node, _num);

        _retMap.set(node, _num);

        ++_num;

      }

      void discover(const Arc& edge) {

        _predMap.set(_graph.target(edge), _graph.source(edge));

      }

      void examine(const Arc& edge) {

        if (_graph.source(edge) == _graph.target(edge) &&

            _graph.direction(edge)) {

          if (!_cutMap[_graph.source(edge)]) {

            _cutMap.set(_graph.source(edge), true);

            ++_cutNum;

          }

          return;

        }

        if (_predMap[_graph.source(edge)] == _graph.target(edge)) return;

        if (_retMap[_graph.source(edge)] > _numMap[_graph.target(edge)]) {

          _retMap.set(_graph.source(edge), _numMap[_graph.target(edge)]);

        }

      }

      void backtrack(const Arc& edge) {

        if (_retMap[_graph.source(edge)] > _retMap[_graph.target(edge)]) {

          _retMap.set(_graph.source(edge), _retMap[_graph.target(edge)]);

        }

        if (_numMap[_graph.source(edge)] <= _retMap[_graph.target(edge)]) {

          if (_predMap[_graph.source(edge)] != INVALID) {

            if (!_cutMap[_graph.source(edge)]) {

              _cutMap.set(_graph.source(edge), true);

              ++_cutNum;

            }

          } else if (rootCut) {

            if (!_cutMap[_graph.source(edge)]) {

              _cutMap.set(_graph.source(edge), true);

              ++_cutNum;

            }

          } else {

            rootCut = true;

          }

        }

      }

    private:

      const Digraph& _graph;

      NodeMap& _cutMap;

      int& _cutNum;

      typename Digraph::template NodeMap<int> _numMap;

      typename Digraph::template NodeMap<int> _retMap;

      typename Digraph::template NodeMap<Node> _predMap;

      std::stack<Edge> _edgeStack;

      int _num;

      bool rootCut;

    };

  }

  template <typename Graph>

  int countBiNodeConnectedComponents(const Graph& graph);

  /// \ingroup connectivity

  ///

  /// \brief Checks the graph is bi-node-connected.

  ///

  /// This function checks that the undirected graph is bi-node-connected

  /// graph. The graph is bi-node-connected if any two undirected edge is

  /// on same circle.

  ///

  /// \param graph The graph.

  /// \return %True when the graph bi-node-connected.

  template <typename Graph>

  bool biNodeConnected(const Graph& graph) {

    return countBiNodeConnectedComponents(graph) <= 1;

  }

  /// \ingroup connectivity

  ///

  /// \brief Count the biconnected components.

  ///

  /// This function finds the bi-node-connected components in an undirected

  /// graph. The biconnected components are the classes of an equivalence

  /// relation on the undirected edges. Two undirected edge is in relationship

  /// when they are on same circle.

  ///

  /// \param graph The graph.

  /// \return The number of components.

  template <typename Graph>

  int countBiNodeConnectedComponents(const Graph& graph) {

    checkConcept<concepts::Graph, Graph>();

    typedef typename Graph::NodeIt NodeIt;

    using namespace _topology_bits;

    typedef CountBiNodeConnectedComponentsVisitor<Graph> Visitor;

    int compNum = 0;

    Visitor visitor(graph, compNum);

    DfsVisit<Graph, Visitor> dfs(graph, visitor);

    dfs.init();

    for (NodeIt it(graph); it != INVALID; ++it) {

      if (!dfs.reached(it)) {

        dfs.addSource(it);

        dfs.start();

      }

    }

    return compNum;

  }

  /// \ingroup connectivity

  ///

  /// \brief Find the bi-node-connected components.

  ///

  /// This function finds the bi-node-connected components in an undirected

  /// graph. The bi-node-connected components are the classes of an equivalence

  /// relation on the undirected edges. Two undirected edge are in relationship

  /// when they are on same circle.

  ///

  /// \param graph The graph.

  /// \retval compMap A writable uedge map. The values will be set from 0

  /// to the number of the biconnected components minus one. Each values

  /// of the map will be set exactly once, the values of a certain component

  /// will be set continuously.

  /// \return The number of components.

  ///

  template <typename Graph, typename EdgeMap>

  int biNodeConnectedComponents(const Graph& graph,

                                EdgeMap& compMap) {

    checkConcept<concepts::Graph, Graph>();

    typedef typename Graph::NodeIt NodeIt;

    typedef typename Graph::Edge Edge;

    checkConcept<concepts::WriteMap<Edge, int>, EdgeMap>();

    using namespace _topology_bits;

    typedef BiNodeConnectedComponentsVisitor<Graph, EdgeMap> Visitor;

    int compNum = 0;

    Visitor visitor(graph, compMap, compNum);

    DfsVisit<Graph, Visitor> dfs(graph, visitor);

    dfs.init();

    for (NodeIt it(graph); it != INVALID; ++it) {

      if (!dfs.reached(it)) {

        dfs.addSource(it);

        dfs.start();

      }

    }

    return compNum;

  }

  /// \ingroup connectivity

  ///

  /// \brief Find the bi-node-connected cut nodes.

  ///

  /// This function finds the bi-node-connected cut nodes in an undirected

  /// graph. The bi-node-connected components are the classes of an equivalence

  /// relation on the undirected edges. Two undirected edges are in

  /// relationship when they are on same circle. The biconnected components

  /// are separted by nodes which are the cut nodes of the components.

  ///

  /// \param graph The graph.

  /// \retval cutMap A writable edge map. The values will be set true when

  /// the node separate two or more components.

  /// \return The number of the cut nodes.

  template <typename Graph, typename NodeMap>

  int biNodeConnectedCutNodes(const Graph& graph, NodeMap& cutMap) {

    checkConcept<concepts::Graph, Graph>();

    typedef typename Graph::Node Node;

    typedef typename Graph::NodeIt NodeIt;

    checkConcept<concepts::WriteMap<Node, bool>, NodeMap>();

    using namespace _topology_bits;

    typedef BiNodeConnectedCutNodesVisitor<Graph, NodeMap> Visitor;

    int cutNum = 0;

    Visitor visitor(graph, cutMap, cutNum);

    DfsVisit<Graph, Visitor> dfs(graph, visitor);

    dfs.init();

    for (NodeIt it(graph); it != INVALID; ++it) {

      if (!dfs.reached(it)) {

        dfs.addSource(it);

        dfs.start();

      }

    }

    return cutNum;

  }

  namespace _topology_bits {

    template <typename Digraph>

    class CountBiEdgeConnectedComponentsVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      typedef typename Digraph::Arc Arc;

      typedef typename Digraph::Edge Edge;

      CountBiEdgeConnectedComponentsVisitor(const Digraph& graph, int &compNum)

        : _graph(graph), _compNum(compNum),

          _numMap(graph), _retMap(graph), _predMap(graph), _num(0) {}

      void start(const Node& node) {

        _predMap.set(node, INVALID);

      }

      void reach(const Node& node) {

        _numMap.set(node, _num);

        _retMap.set(node, _num);

        ++_num;

      }

      void leave(const Node& node) {

        if (_numMap[node] <= _retMap[node]) {

          ++_compNum;

        }

      }

      void discover(const Arc& edge) {

        _predMap.set(_graph.target(edge), edge);

      }

      void examine(const Arc& edge) {

        if (_predMap[_graph.source(edge)] == _graph.oppositeArc(edge)) {

          return;

        }

        if (_retMap[_graph.source(edge)] > _retMap[_graph.target(edge)]) {

          _retMap.set(_graph.source(edge), _retMap[_graph.target(edge)]);

        }

      }

      void backtrack(const Arc& edge) {

        if (_retMap[_graph.source(edge)] > _retMap[_graph.target(edge)]) {

          _retMap.set(_graph.source(edge), _retMap[_graph.target(edge)]);

        }

      }

    private:

      const Digraph& _graph;

      int& _compNum;

      typename Digraph::template NodeMap<int> _numMap;

      typename Digraph::template NodeMap<int> _retMap;

      typename Digraph::template NodeMap<Arc> _predMap;

      int _num;

    };

    template <typename Digraph, typename NodeMap>

    class BiEdgeConnectedComponentsVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      typedef typename Digraph::Arc Arc;

      typedef typename Digraph::Edge Edge;

      BiEdgeConnectedComponentsVisitor(const Digraph& graph,

                                       NodeMap& compMap, int &compNum)

        : _graph(graph), _compMap(compMap), _compNum(compNum),

          _numMap(graph), _retMap(graph), _predMap(graph), _num(0) {}

      void start(const Node& node) {

        _predMap.set(node, INVALID);

      }

      void reach(const Node& node) {

        _numMap.set(node, _num);

        _retMap.set(node, _num);

        _nodeStack.push(node);

        ++_num;

      }

      void leave(const Node& node) {

        if (_numMap[node] <= _retMap[node]) {

          while (_nodeStack.top() != node) {

            _compMap.set(_nodeStack.top(), _compNum);

            _nodeStack.pop();

          }

          _compMap.set(node, _compNum);

          _nodeStack.pop();

          ++_compNum;

        }

      }

      void discover(const Arc& edge) {

        _predMap.set(_graph.target(edge), edge);

      }

      void examine(const Arc& edge) {

        if (_predMap[_graph.source(edge)] == _graph.oppositeArc(edge)) {

          return;

        }

        if (_retMap[_graph.source(edge)] > _retMap[_graph.target(edge)]) {

          _retMap.set(_graph.source(edge), _retMap[_graph.target(edge)]);

        }

      }

      void backtrack(const Arc& edge) {

        if (_retMap[_graph.source(edge)] > _retMap[_graph.target(edge)]) {

          _retMap.set(_graph.source(edge), _retMap[_graph.target(edge)]);

        }

      }

    private:

      const Digraph& _graph;

      NodeMap& _compMap;

      int& _compNum;

      typename Digraph::template NodeMap<int> _numMap;

      typename Digraph::template NodeMap<int> _retMap;

      typename Digraph::template NodeMap<Arc> _predMap;

      std::stack<Node> _nodeStack;

      int _num;

    };

    template <typename Digraph, typename ArcMap>

    class BiEdgeConnectedCutEdgesVisitor : public DfsVisitor<Digraph> {

    public:

      typedef typename Digraph::Node Node;

      typedef typename Digraph::Arc Arc;

      typedef typename Digraph::Edge Edge;

      BiEdgeConnectedCutEdgesVisitor(const Digraph& graph,

                                     ArcMap& cutMap, int &cutNum)

        : _graph(graph), _cutMap(cutMap), _cutNum(cutNum),

          _numMap(graph), _retMap(graph), _predMap(graph), _num(0) {}

      void start(const Node& node) {

        _predMap[node] = INVALID;

      }

      void reach(const Node& node) {

        _numMap.set(node, _num);

        _retMap.set(node, _num);

        ++_num;

      }

      void leave(const Node& node) {

        if (_numMap[node] <= _retMap[node]) {

          if (_predMap[node] != INVALID) {

            _cutMap.set(_predMap[node], true);

            ++_cutNum;

          }

        }

      }

      void discover(const Arc& edge) {

        _predMap.set(_graph.target(edge), edge);

      }