/* -*- 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_STEINER_H

 #define LEMON_STEINER_H

 ///\ingroup approx

 ///\file

 ///\brief Algorithm for the 2-approximation of Steiner Tree problem.

 ///

 #include <lemon/smart_graph.h>

 #include <lemon/graph_utils.h>

 #include <lemon/error.h>

 #include <lemon/ugraph_adaptor.h>

 #include <lemon/maps.h>

 #include <lemon/dijkstra.h>

 #include <lemon/prim.h>

 namespace lemon {

   /// \ingroup approx

   /// \brief Algorithm for the 2-approximation of Steiner Tree problem

   ///

   /// The Steiner-tree problem is the next: Given a connected

   /// undirected graph, a cost function on the edges and a subset of

   /// the nodes. Construct a tree with minimum cost which covers the

   /// given subset of the nodes. The problem is NP-hard moreover

   /// it is APX-complete too.

   ///

   /// Mehlhorn's approximation algorithm is implemented in this class,

   /// which gives a 2-approximation for the Steiner-tree problem. The

   /// algorithm's time complexity is O(nlog(n)+e).

   template <typename UGraph,

             typename CostMap = typename UGraph:: template UEdgeMap<double> >

   class SteinerTree {

   public:

     UGRAPH_TYPEDEFS(typename UGraph)

     typedef typename CostMap::Value Value;

   private:

     class CompMap {

     public:

       typedef Node Key;

       typedef Edge Value;

     private:

       const UGraph& _graph;

       typename UGraph::template NodeMap<int> _comp;

     public:

       CompMap(const UGraph& graph) : _graph(graph), _comp(graph) {}

       void set(const Node& node, const Edge& edge) {

         if (edge != INVALID) {

           _comp.set(node, _comp[_graph.source(edge)]);

         } else {

           _comp.set(node, -1);

         }

       }

       int comp(const Node& node) const { return _comp[node]; }

       void comp(const Node& node, int value) { _comp.set(node, value); }

     };

     typedef typename UGraph::template NodeMap<Edge> PredMap;

     typedef ForkWriteMap<PredMap, CompMap> ForkedMap;

     struct External {

       int source, target;

       UEdge uedge;

       Value value;

       External(int s, int t, const UEdge& e, const Value& v)

         : source(s), target(t), uedge(e), value(v) {}

     };

     struct ExternalLess {

       bool operator()(const External& left, const External& right) const {

         return (left.source < right.source) || 

           (left.source == right.source && left.target < right.target);

       }

     };

     typedef typename UGraph::template NodeMap<bool> FilterMap;

     typedef typename UGraph::template UEdgeMap<bool> TreeMap;

     const UGraph& _graph;

     const CostMap& _cost;

     typename Dijkstra<UGraph, CostMap>::

     template DefPredMap<ForkedMap>::Create _dijkstra;

     PredMap* _pred;

     CompMap* _comp;

     ForkedMap* _forked;

     int _terminal_num;

     FilterMap *_filter;

     TreeMap *_tree;

   public:

     /// \brief Constructor

     /// Constructor

     ///

     SteinerTree(const UGraph &graph, const CostMap &cost)

       : _graph(graph), _cost(cost), _dijkstra(graph, _cost), 

         _pred(0), _comp(0), _forked(0), _filter(0), _tree(0) {}

     /// \brief Initializes the internal data structures.

     ///

     /// Initializes the internal data structures.

     void init() {

       if (!_pred) _pred = new PredMap(_graph);

       if (!_comp) _comp = new CompMap(_graph);

       if (!_forked) _forked = new ForkedMap(*_pred, *_comp);

       if (!_filter) _filter = new FilterMap(_graph);

       if (!_tree) _tree = new TreeMap(_graph);

       _dijkstra.predMap(*_forked);

       _dijkstra.init();

       _terminal_num = 0;

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

         _filter->set(it, false);

       }

     }

     /// \brief Adds a new terminal node.

     ///

     /// Adds a new terminal node to the Steiner-tree problem.

     void addTerminal(const Node& node) {

       if (!_dijkstra.reached(node)) {

         _dijkstra.addSource(node);

         _comp->comp(node, _terminal_num);

         ++_terminal_num;

       }

     }

     /// \brief Executes the algorithm.

     ///

     /// Executes the algorithm.

     ///

     /// \pre init() must be called and at least some nodes should be

     /// added with addTerminal() before using this function.

     ///

     /// This method constructs an approximation of the Steiner-Tree.

     void start() {

       _dijkstra.start();

       std::vector<External> externals;

       for (UEdgeIt it(_graph); it != INVALID; ++it) {

         Node s = _graph.source(it);

         Node t = _graph.target(it);

         if (_comp->comp(s) == _comp->comp(t)) continue;

         Value cost = _dijkstra.dist(s) + _dijkstra.dist(t) + _cost[it];

         if (_comp->comp(s) < _comp->comp(t)) {

           externals.push_back(External(_comp->comp(s), _comp->comp(t), 

                                        it, cost));

         } else {

           externals.push_back(External(_comp->comp(t), _comp->comp(s), 

                                        it, cost));

         }

       }

       std::sort(externals.begin(), externals.end(), ExternalLess());

       SmartUGraph aux_graph;

       std::vector<SmartUGraph::Node> aux_nodes;

       for (int i = 0; i < _terminal_num; ++i) {

         aux_nodes.push_back(aux_graph.addNode());

       }

       SmartUGraph::UEdgeMap<Value> aux_cost(aux_graph);

       SmartUGraph::UEdgeMap<UEdge> cross(aux_graph);

       {

         int i = 0;

         while (i < int(externals.size())) {

           int sn = externals[i].source;

           int tn = externals[i].target;

           Value ev = externals[i].value;

           UEdge ee = externals[i].uedge;

           ++i;

           while (i < int(externals.size()) && 

                  sn == externals[i].source && tn == externals[i].target) {

             if (externals[i].value < ev) {

               ev = externals[i].value;

               ee = externals[i].uedge;

             }

             ++i;

           }

           SmartUGraph::UEdge ne = 

             aux_graph.addEdge(aux_nodes[sn], aux_nodes[tn]);

           aux_cost.set(ne, ev);

           cross.set(ne, ee);

         }

       }

       std::vector<SmartUGraph::UEdge> aux_tree_edges;

       BackInserterBoolMap<std::vector<SmartUGraph::UEdge> >

         aux_tree_map(aux_tree_edges);

       prim(aux_graph, aux_cost, aux_tree_map);

       for (std::vector<SmartUGraph::UEdge>::iterator 

              it = aux_tree_edges.begin(); it != aux_tree_edges.end(); ++it) {

         Node node;

         node = _graph.source(cross[*it]);

         while (node != INVALID && !(*_filter)[node]) {

           _filter->set(node, true);

           node = (*_pred)[node] != INVALID ? 

             _graph.source((*_pred)[node]) : INVALID;

         }

         node = _graph.target(cross[*it]);

         while (node != INVALID && !(*_filter)[node]) {

           _filter->set(node, true);

           node = (*_pred)[node] != INVALID ? 

             _graph.source((*_pred)[node]) : INVALID;

         }

       }

       prim(nodeSubUGraphAdaptor(_graph, *_filter), _cost, *_tree);

     }

     /// \brief Checks if an edge is in the Steiner-tree or not.

     ///

     /// Checks if an edge is in the Steiner-tree or not.

     /// \param e is the edge that will be checked

     /// \return \c true if e is in the Steiner-tree, \c false otherwise

     bool tree(UEdge e){

       return (*_tree)[e];

     }

     /// \brief Checks if the node is in the Steiner-tree or not.

     ///

     /// Checks if a node is in the Steiner-tree or not.

     /// \param n is the node that will be checked

     /// \return \c true if n is in the Steiner-tree, \c false otherwise

     bool tree(Node n){

       return (*_filter)[n];

     }

   };

 } //END OF NAMESPACE LEMON

 #endif