/* -*- C++ -*-

  *

  * 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_GOMORY_HU_TREE_H

 #define LEMON_GOMORY_HU_TREE_H

 #include <limits>

 #include <lemon/core.h>

 #include <lemon/preflow.h>

 #include <lemon/concept_check.h>

 #include <lemon/concepts/maps.h>

 /// \ingroup min_cut

 /// \file 

 /// \brief Gomory-Hu cut tree in graphs.

 namespace lemon {

   /// \ingroup min_cut

   ///

   /// \brief Gomory-Hu cut tree algorithm

   ///

   /// The Gomory-Hu tree is a tree on the node set of a given graph, but it

   /// may contain edges which are not in the original graph. It has the

   /// property that the minimum capacity edge of the path between two nodes 

   /// in this tree has the same weight as the minimum cut in the graph

   /// between these nodes. Moreover the components obtained by removing

   /// this edge from the tree determine the corresponding minimum cut.

   ///

   /// Therefore once this tree is computed, the minimum cut between any pair

   /// of nodes can easily be obtained.

   /// 

   /// The algorithm calculates \e n-1 distinct minimum cuts (currently with

   /// the \ref Preflow algorithm), therefore the algorithm has

   /// \f$(O(n^3\sqrt{e})\f$ overall time complexity. It calculates a

   /// rooted Gomory-Hu tree, its structure and the weights can be obtained

   /// by \c predNode(), \c predValue() and \c rootDist().

   /// 

   /// The members \c minCutMap() and \c minCutValue() calculate

   /// the minimum cut and the minimum cut value between any two nodes

   /// in the graph. You can also list (iterate on) the nodes and the

   /// edges of the cuts using \c MinCutNodeIt and \c MinCutEdgeIt.

   ///

   /// \tparam GR The type of the undirected graph the algorithm runs on.

   /// \tparam CAP The type of the edge map describing the edge capacities.

   /// It is \ref concepts::Graph::EdgeMap "GR::EdgeMap<int>" by default.

 #ifdef DOXYGEN

   template <typename GR,

 	    typename CAP>

 #else

   template <typename GR,

 	    typename CAP = typename GR::template EdgeMap<int> >

 #endif

   class GomoryHu {

   public:

     /// The graph type

     typedef GR Graph;

     /// The type of the edge capacity map

     typedef CAP Capacity;

     /// The value type of capacities

     typedef typename Capacity::Value Value;

   private:

     TEMPLATE_GRAPH_TYPEDEFS(Graph);

     const Graph& _graph;

     const Capacity& _capacity;

     Node _root;

     typename Graph::template NodeMap<Node>* _pred;

     typename Graph::template NodeMap<Value>* _weight;

     typename Graph::template NodeMap<int>* _order;

     void createStructures() {

       if (!_pred) {

 	_pred = new typename Graph::template NodeMap<Node>(_graph);

       }

       if (!_weight) {

 	_weight = new typename Graph::template NodeMap<Value>(_graph);

       }

       if (!_order) {

 	_order = new typename Graph::template NodeMap<int>(_graph);

       }

     }

     void destroyStructures() {

       if (_pred) {

 	delete _pred;

       }

       if (_weight) {

 	delete _weight;

       }

       if (_order) {

 	delete _order;

       }

     }

   public:

     /// \brief Constructor

     ///

     /// Constructor

     /// \param graph The undirected graph the algorithm runs on.

     /// \param capacity The edge capacity map.

     GomoryHu(const Graph& graph, const Capacity& capacity) 

       : _graph(graph), _capacity(capacity),

 	_pred(0), _weight(0), _order(0) 

     {

       checkConcept<concepts::ReadMap<Edge, Value>, Capacity>();

     }

     /// \brief Destructor

     ///

     /// Destructor

     ~GomoryHu() {

       destroyStructures();

     }

   private:

     // Initialize the internal data structures

     void init() {

       createStructures();

       _root = NodeIt(_graph);

       for (NodeIt n(_graph); n != INVALID; ++n) {

 	_pred->set(n, _root);

 	_order->set(n, -1);

       }

       _pred->set(_root, INVALID);

       _weight->set(_root, std::numeric_limits<Value>::max()); 

     }

     // Start the algorithm

     void start() {

       Preflow<Graph, Capacity> fa(_graph, _capacity, _root, INVALID);

       for (NodeIt n(_graph); n != INVALID; ++n) {

 	if (n == _root) continue;

 	Node pn = (*_pred)[n];

 	fa.source(n);

 	fa.target(pn);

 	fa.runMinCut();

 	_weight->set(n, fa.flowValue());

 	for (NodeIt nn(_graph); nn != INVALID; ++nn) {

 	  if (nn != n && fa.minCut(nn) && (*_pred)[nn] == pn) {

 	    _pred->set(nn, n);

 	  }

 	}

 	if ((*_pred)[pn] != INVALID && fa.minCut((*_pred)[pn])) {

 	  _pred->set(n, (*_pred)[pn]);

 	  _pred->set(pn, n);

 	  _weight->set(n, (*_weight)[pn]);

 	  _weight->set(pn, fa.flowValue());	

 	}

       }

       _order->set(_root, 0);

       int index = 1;

       for (NodeIt n(_graph); n != INVALID; ++n) {

 	std::vector<Node> st;

 	Node nn = n;

 	while ((*_order)[nn] == -1) {

 	  st.push_back(nn);

 	  nn = (*_pred)[nn];

 	}

 	while (!st.empty()) {

 	  _order->set(st.back(), index++);

 	  st.pop_back();

 	}

       }

     }

   public:

     ///\name Execution Control

     ///@{

     /// \brief Run the Gomory-Hu algorithm.

     ///

     /// This function runs the Gomory-Hu algorithm.

     void run() {

       init();

       start();

     }

     /// @}

     ///\name Query Functions

     ///The results of the algorithm can be obtained using these

     ///functions.\n

     ///\ref run() "run()" should be called before using them.\n

     ///See also \ref MinCutNodeIt and \ref MinCutEdgeIt.

     ///@{

     /// \brief Return the predecessor node in the Gomory-Hu tree.

     ///

     /// This function returns the predecessor node in the Gomory-Hu tree.

     /// If the node is

     /// the root of the Gomory-Hu tree, then it returns \c INVALID.

     Node predNode(const Node& node) {

       return (*_pred)[node];

     }

     /// \brief Return the distance from the root node in the Gomory-Hu tree.

     ///

     /// This function returns the distance of \c node from the root node

     /// in the Gomory-Hu tree.

     int rootDist(const Node& node) {

       return (*_order)[node];

     }

     /// \brief Return the weight of the predecessor edge in the

     /// Gomory-Hu tree.

     ///

     /// This function returns the weight of the predecessor edge in the

     /// Gomory-Hu tree.  If the node is the root, the result is undefined.

     Value predValue(const Node& node) {

       return (*_weight)[node];

     }

     /// \brief Return the minimum cut value between two nodes

     ///

     /// This function returns the minimum cut value between two nodes. The

     /// algorithm finds the nearest common ancestor in the Gomory-Hu

     /// tree and calculates the minimum weight edge on the paths to

     /// the ancestor.

     Value minCutValue(const Node& s, const Node& t) const {

       Node sn = s, tn = t;

       Value value = std::numeric_limits<Value>::max();

       while (sn != tn) {

 	if ((*_order)[sn] < (*_order)[tn]) {

 	  if ((*_weight)[tn] <= value) value = (*_weight)[tn];

 	  tn = (*_pred)[tn];

 	} else {

 	  if ((*_weight)[sn] <= value) value = (*_weight)[sn];

 	  sn = (*_pred)[sn];

 	}

       }

       return value;

     }

     /// \brief Return the minimum cut between two nodes

     ///

     /// This function returns the minimum cut between the nodes \c s and \c t

     /// in the \c cutMap parameter by setting the nodes in the component of

     /// \c s to \c true and the other nodes to \c false.

     ///

     /// For higher level interfaces, see MinCutNodeIt and MinCutEdgeIt.

     template <typename CutMap>

     Value minCutMap(const Node& s, ///< The base node.

                     const Node& t,

                     ///< The node you want to separate from node \c s.

                     CutMap& cutMap

                     ///< The cut will be returned in this map.

                     /// It must be a \c bool (or convertible) 

                     /// \ref concepts::ReadWriteMap "ReadWriteMap"

                     /// on the graph nodes.

                     ) const {

       Node sn = s, tn = t;

       bool s_root=false;

       Node rn = INVALID;

       Value value = std::numeric_limits<Value>::max();

       while (sn != tn) {

 	if ((*_order)[sn] < (*_order)[tn]) {

 	  if ((*_weight)[tn] <= value) {

 	    rn = tn;

             s_root = false;

 	    value = (*_weight)[tn];

 	  }

 	  tn = (*_pred)[tn];

 	} else {

 	  if ((*_weight)[sn] <= value) {

 	    rn = sn;

             s_root = true;

 	    value = (*_weight)[sn];

 	  }

 	  sn = (*_pred)[sn];

 	}

       }

       typename Graph::template NodeMap<bool> reached(_graph, false);

       reached.set(_root, true);

       cutMap.set(_root, !s_root);

       reached.set(rn, true);

       cutMap.set(rn, s_root);

       std::vector<Node> st;

       for (NodeIt n(_graph); n != INVALID; ++n) {

 	st.clear();

         Node nn = n;

 	while (!reached[nn]) {

 	  st.push_back(nn);

 	  nn = (*_pred)[nn];

 	}

 	while (!st.empty()) {

 	  cutMap.set(st.back(), cutMap[nn]);

 	  st.pop_back();

 	}

       }

       return value;

     }

     ///@}

     friend class MinCutNodeIt;

     /// Iterate on the nodes of a minimum cut

     /// This iterator class lists the nodes of a minimum cut found by

     /// GomoryHu. Before using it, you must allocate a GomoryHu class,

     /// and call its \ref GomoryHu::run() "run()" method.

     ///

     /// This example counts the nodes in the minimum cut separating \c s from

     /// \c t.

     /// \code

     /// GomoruHu<Graph> gom(g, capacities);

     /// gom.run();

     /// int cnt=0;

     /// for(GomoruHu<Graph>::MinCutNodeIt n(gom,s,t); n!=INVALID; ++n) ++cnt;

     /// \endcode

     class MinCutNodeIt

     {

       bool _side;

       typename Graph::NodeIt _node_it;

       typename Graph::template NodeMap<bool> _cut;

     public:

       /// Constructor

       /// Constructor.

       ///

       MinCutNodeIt(GomoryHu const &gomory,

                    ///< The GomoryHu class. You must call its

                    ///  run() method

                    ///  before initializing this iterator.

                    const Node& s, ///< The base node.

                    const Node& t,

                    ///< The node you want to separate from node \c s.

                    bool side=true

                    ///< If it is \c true (default) then the iterator lists

                    ///  the nodes of the component containing \c s,

                    ///  otherwise it lists the other component.

                    /// \note As the minimum cut is not always unique,

                    /// \code

                    /// MinCutNodeIt(gomory, s, t, true);

                    /// \endcode

                    /// and

                    /// \code

                    /// MinCutNodeIt(gomory, t, s, false);

                    /// \endcode

                    /// does not necessarily give the same set of nodes.

                    /// However it is ensured that

                    /// \code

                    /// MinCutNodeIt(gomory, s, t, true);

                    /// \endcode

                    /// and

                    /// \code

                    /// MinCutNodeIt(gomory, s, t, false);

                    /// \endcode

                    /// together list each node exactly once.

                    )

         : _side(side), _cut(gomory._graph)

       {

         gomory.minCutMap(s,t,_cut);

         for(_node_it=typename Graph::NodeIt(gomory._graph);

             _node_it!=INVALID && _cut[_node_it]!=_side;

             ++_node_it) {}

       }

       /// Conversion to \c Node

       /// Conversion to \c Node.

       ///

       operator typename Graph::Node() const

       {

         return _node_it;

       }

       bool operator==(Invalid) { return _node_it==INVALID; }

       bool operator!=(Invalid) { return _node_it!=INVALID; }

       /// Next node

       /// Next node.

       ///

       MinCutNodeIt &operator++()

       {

         for(++_node_it;_node_it!=INVALID&&_cut[_node_it]!=_side;++_node_it) {}

         return *this;

       }

       /// Postfix incrementation

       /// Postfix incrementation.

       ///

       /// \warning This incrementation

       /// returns a \c Node, not a \c MinCutNodeIt, as one may

       /// expect.

       typename Graph::Node operator++(int)

       {

         typename Graph::Node n=*this;

         ++(*this);

         return n;

       }

     };

     friend class MinCutEdgeIt;

     /// Iterate on the edges of a minimum cut

     /// This iterator class lists the edges of a minimum cut found by

     /// GomoryHu. Before using it, you must allocate a GomoryHu class,

     /// and call its \ref GomoryHu::run() "run()" method.

     ///

     /// This example computes the value of the minimum cut separating \c s from

     /// \c t.

     /// \code

     /// GomoruHu<Graph> gom(g, capacities);

     /// gom.run();

     /// int value=0;

     /// for(GomoruHu<Graph>::MinCutEdgeIt e(gom,s,t); e!=INVALID; ++e)

     ///   value+=capacities[e];

     /// \endcode

     /// the result will be the same as it is returned by

     /// \ref GomoryHu::minCutValue() "gom.minCutValue(s,t)"

     class MinCutEdgeIt

     {

       bool _side;

       const Graph &_graph;

       typename Graph::NodeIt _node_it;

       typename Graph::OutArcIt _arc_it;

       typename Graph::template NodeMap<bool> _cut;

       void step()

       {

         ++_arc_it;

         while(_node_it!=INVALID && _arc_it==INVALID)

           {

             for(++_node_it;_node_it!=INVALID&&!_cut[_node_it];++_node_it) {}

             if(_node_it!=INVALID)

               _arc_it=typename Graph::OutArcIt(_graph,_node_it);

           }

       }

     public:

       MinCutEdgeIt(GomoryHu const &gomory,

                    ///< The GomoryHu class. You must call its

                    ///  run() method

                    ///  before initializing this iterator.

                    const Node& s,  ///< The base node.

                    const Node& t,

                    ///< The node you want to separate from node \c s.

                    bool side=true

                    ///< If it is \c true (default) then the listed arcs

                    ///  will be oriented from the

                    ///  the nodes of the component containing \c s,

                    ///  otherwise they will be oriented in the opposite

                    ///  direction.

                    )

         : _graph(gomory._graph), _cut(_graph)

       {

         gomory.minCutMap(s,t,_cut);

         if(!side)

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

             _cut[n]=!_cut[n];

         for(_node_it=typename Graph::NodeIt(_graph);

             _node_it!=INVALID && !_cut[_node_it];

             ++_node_it) {}

         _arc_it = _node_it!=INVALID ?

           typename Graph::OutArcIt(_graph,_node_it) : INVALID;

         while(_node_it!=INVALID && _arc_it == INVALID)

           {

             for(++_node_it; _node_it!=INVALID&&!_cut[_node_it]; ++_node_it) {}

             if(_node_it!=INVALID)

               _arc_it= typename Graph::OutArcIt(_graph,_node_it);

           }

         while(_arc_it!=INVALID && _cut[_graph.target(_arc_it)]) step();

       }

       /// Conversion to \c Arc

       /// Conversion to \c Arc.

       ///

       operator typename Graph::Arc() const

       {

         return _arc_it;

       }

       /// Conversion to \c Edge

       /// Conversion to \c Edge.

       ///

       operator typename Graph::Edge() const

       {

         return _arc_it;

       }

       bool operator==(Invalid) { return _node_it==INVALID; }

       bool operator!=(Invalid) { return _node_it!=INVALID; }

       /// Next edge

       /// Next edge.

       ///

       MinCutEdgeIt &operator++()

       {

         step();

         while(_arc_it!=INVALID && _cut[_graph.target(_arc_it)]) step();

         return *this;

       }

       /// Postfix incrementation

       /// Postfix incrementation.

       ///

       /// \warning This incrementation

       /// returns an \c Arc, not a \c MinCutEdgeIt, as one may expect.

       typename Graph::Arc operator++(int)

       {

         typename Graph::Arc e=*this;

         ++(*this);

         return e;

       }

     };

   };

 }

 #endif