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

  *

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

  *

  * Copyright (C) 2003-2013

  * 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_NEAREST_NEIGHBOUR_TSP_H

 #define LEMON_NEAREST_NEIGHBOUR_TSP_H

 /// \ingroup tsp

 /// \file

 /// \brief Nearest neighbor algorithm for symmetric TSP

 #include <deque>

 #include <vector>

 #include <limits>

 #include <lemon/full_graph.h>

 #include <lemon/maps.h>

 namespace lemon {

   /// \ingroup tsp

   ///

   /// \brief Nearest neighbor algorithm for symmetric TSP.

   ///

   /// NearestNeighborTsp implements the nearest neighbor heuristic for solving

   /// symmetric \ref tsp "TSP".

   ///

   /// This is probably the simplest TSP heuristic.

   /// It starts with a minimum cost edge and at each step, it connects the

   /// nearest unvisited node to the current path.

   /// Finally, it connects the two end points of the path to form a tour.

   ///

   /// This method runs in O(n<sup>2</sup>) time.

   /// It quickly finds a relatively short tour for most TSP instances,

   /// but it could also yield a really bad (or even the worst) solution

   /// in special cases.

   ///

   /// \tparam CM Type of the cost map.

   template <typename CM>

   class NearestNeighborTsp

   {

     public:

       /// Type of the cost map

       typedef CM CostMap;

       /// Type of the edge costs

       typedef typename CM::Value Cost;

     private:

       GRAPH_TYPEDEFS(FullGraph);

       const FullGraph &_gr;

       const CostMap &_cost;

       Cost _sum;

       std::vector<Node> _path;

     public:

       /// \brief Constructor

       ///

       /// Constructor.

       /// \param gr The \ref FullGraph "full graph" the algorithm runs on.

       /// \param cost The cost map.

       NearestNeighborTsp(const FullGraph &gr, const CostMap &cost)

         : _gr(gr), _cost(cost) {}

       /// \name Execution Control

       /// @{

       /// \brief Runs the algorithm.

       ///

       /// This function runs the algorithm.

       ///

       /// \return The total cost of the found tour.

       Cost run() {

         _path.clear();

         if (_gr.nodeNum() == 0) {

           return _sum = 0;

         }

         else if (_gr.nodeNum() == 1) {

           _path.push_back(_gr(0));

           return _sum = 0;

         }

         std::deque<Node> path_dq;

         Edge min_edge1 = INVALID,

              min_edge2 = INVALID;

         min_edge1 = mapMin(_gr, _cost);

         Node n1 = _gr.u(min_edge1),

              n2 = _gr.v(min_edge1);

         path_dq.push_back(n1);

         path_dq.push_back(n2);

         FullGraph::NodeMap<bool> used(_gr, false);

         used[n1] = true;

         used[n2] = true;

         min_edge1 = INVALID;

         while (int(path_dq.size()) != _gr.nodeNum()) {

           if (min_edge1 == INVALID) {

             for (IncEdgeIt e(_gr, n1); e != INVALID; ++e) {

               if (!used[_gr.runningNode(e)] &&

                   (_cost[e] < _cost[min_edge1] || min_edge1 == INVALID)) {

                 min_edge1 = e;

               }

             }

           }

           if (min_edge2 == INVALID) {

             for (IncEdgeIt e(_gr, n2); e != INVALID; ++e) {

               if (!used[_gr.runningNode(e)] &&

                   (_cost[e] < _cost[min_edge2] || min_edge2 == INVALID)) {

                 min_edge2 = e;

               }

             }

           }

           if (_cost[min_edge1] < _cost[min_edge2]) {

             n1 = _gr.oppositeNode(n1, min_edge1);

             path_dq.push_front(n1);

             used[n1] = true;

             min_edge1 = INVALID;

             if (_gr.u(min_edge2) == n1 || _gr.v(min_edge2) == n1)

               min_edge2 = INVALID;

           } else {

             n2 = _gr.oppositeNode(n2, min_edge2);

             path_dq.push_back(n2);

             used[n2] = true;

             min_edge2 = INVALID;

             if (_gr.u(min_edge1) == n2 || _gr.v(min_edge1) == n2)

               min_edge1 = INVALID;

           }

         }

         n1 = path_dq.back();

         n2 = path_dq.front();

         _path.push_back(n2);

         _sum = _cost[_gr.edge(n1, n2)];

         for (int i = 1; i < int(path_dq.size()); ++i) {

           n1 = n2;

           n2 = path_dq[i];

           _path.push_back(n2);

           _sum += _cost[_gr.edge(n1, n2)];

         }

         return _sum;

       }

       /// @}

       /// \name Query Functions

       /// @{

       /// \brief The total cost of the found tour.

       ///

       /// This function returns the total cost of the found tour.

       ///

       /// \pre run() must be called before using this function.

       Cost tourCost() const {

         return _sum;

       }

       /// \brief Returns a const reference to the node sequence of the

       /// found tour.

       ///

       /// This function returns a const reference to a vector

       /// that stores the node sequence of the found tour.

       ///

       /// \pre run() must be called before using this function.

       const std::vector<Node>& tourNodes() const {

         return _path;

       }

       /// \brief Gives back the node sequence of the found tour.

       ///

       /// This function copies the node sequence of the found tour into

       /// an STL container through the given output iterator. The

       /// <tt>value_type</tt> of the container must be <tt>FullGraph::Node</tt>.

       /// For example,

       /// \code

       /// std::vector<FullGraph::Node> nodes(countNodes(graph));

       /// tsp.tourNodes(nodes.begin());

       /// \endcode

       /// or

       /// \code

       /// std::list<FullGraph::Node> nodes;

       /// tsp.tourNodes(std::back_inserter(nodes));

       /// \endcode

       ///

       /// \pre run() must be called before using this function.

       template <typename Iterator>

       void tourNodes(Iterator out) const {

         std::copy(_path.begin(), _path.end(), out);

       }

       /// \brief Gives back the found tour as a path.

       ///

       /// This function copies the found tour as a list of arcs/edges into

       /// the given \ref lemon::concepts::Path "path structure".

       ///

       /// \pre run() must be called before using this function.

       template <typename Path>

       void tour(Path &path) const {

         path.clear();

         for (int i = 0; i < int(_path.size()) - 1; ++i) {

           path.addBack(_gr.arc(_path[i], _path[i+1]));

         }

         if (int(_path.size()) >= 2) {

           path.addBack(_gr.arc(_path.back(), _path.front()));

         }

       }

       /// @}

   };

 }; // namespace lemon

 #endif