/* -*- 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)] &&

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

                min_edge1 = e;

              }

            }

          }

          if (min_edge2 == INVALID) {

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

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

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

                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