kpeter@1033: /* -*- mode: C++; indent-tabs-mode: nil; -*-
kpeter@1033:  *
kpeter@1033:  * This file is a part of LEMON, a generic C++ optimization library.
kpeter@1033:  *
alpar@1092:  * Copyright (C) 2003-2013
kpeter@1033:  * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
kpeter@1033:  * (Egervary Research Group on Combinatorial Optimization, EGRES).
kpeter@1033:  *
kpeter@1033:  * Permission to use, modify and distribute this software is granted
kpeter@1033:  * provided that this copyright notice appears in all copies. For
kpeter@1033:  * precise terms see the accompanying LICENSE file.
kpeter@1033:  *
kpeter@1033:  * This software is provided "AS IS" with no warranty of any kind,
kpeter@1033:  * express or implied, and with no claim as to its suitability for any
kpeter@1033:  * purpose.
kpeter@1033:  *
kpeter@1033:  */
kpeter@1033: 
f4c3@1031: #ifndef LEMON_NEAREST_NEIGHBOUR_TSP_H
f4c3@1031: #define LEMON_NEAREST_NEIGHBOUR_TSP_H
f4c3@1031: 
kpeter@1033: /// \ingroup tsp
kpeter@1033: /// \file
kpeter@1033: /// \brief Nearest neighbor algorithm for symmetric TSP
kpeter@1033: 
f4c3@1031: #include <deque>
kpeter@1034: #include <vector>
kpeter@1033: #include <limits>
f4c3@1031: #include <lemon/full_graph.h>
f4c3@1031: #include <lemon/maps.h>
f4c3@1031: 
f4c3@1031: namespace lemon {
f4c3@1031: 
kpeter@1034:   /// \ingroup tsp
kpeter@1034:   ///
kpeter@1033:   /// \brief Nearest neighbor algorithm for symmetric TSP.
kpeter@1033:   ///
kpeter@1033:   /// NearestNeighborTsp implements the nearest neighbor heuristic for solving
kpeter@1033:   /// symmetric \ref tsp "TSP".
kpeter@1033:   ///
kpeter@1033:   /// This is probably the simplest TSP heuristic.
kpeter@1033:   /// It starts with a minimum cost edge and at each step, it connects the
kpeter@1033:   /// nearest unvisited node to the current path.
kpeter@1033:   /// Finally, it connects the two end points of the path to form a tour.
kpeter@1033:   ///
kpeter@1033:   /// This method runs in O(n<sup>2</sup>) time.
kpeter@1036:   /// It quickly finds a relatively short tour for most TSP instances,
kpeter@1036:   /// but it could also yield a really bad (or even the worst) solution
kpeter@1036:   /// in special cases.
kpeter@1033:   ///
kpeter@1033:   /// \tparam CM Type of the cost map.
f4c3@1031:   template <typename CM>
kpeter@1033:   class NearestNeighborTsp
kpeter@1033:   {
kpeter@1033:     public:
kpeter@1033: 
kpeter@1033:       /// Type of the cost map
kpeter@1033:       typedef CM CostMap;
kpeter@1033:       /// Type of the edge costs
kpeter@1033:       typedef typename CM::Value Cost;
kpeter@1033: 
f4c3@1031:     private:
kpeter@1033: 
f4c3@1031:       GRAPH_TYPEDEFS(FullGraph);
f4c3@1031: 
kpeter@1033:       const FullGraph &_gr;
kpeter@1033:       const CostMap &_cost;
kpeter@1033:       Cost _sum;
kpeter@1034:       std::vector<Node> _path;
kpeter@1033: 
f4c3@1031:     public:
f4c3@1031: 
kpeter@1033:       /// \brief Constructor
kpeter@1033:       ///
kpeter@1033:       /// Constructor.
kpeter@1033:       /// \param gr The \ref FullGraph "full graph" the algorithm runs on.
kpeter@1033:       /// \param cost The cost map.
kpeter@1033:       NearestNeighborTsp(const FullGraph &gr, const CostMap &cost)
kpeter@1033:         : _gr(gr), _cost(cost) {}
kpeter@1033: 
kpeter@1033:       /// \name Execution Control
kpeter@1033:       /// @{
kpeter@1033: 
kpeter@1033:       /// \brief Runs the algorithm.
kpeter@1033:       ///
kpeter@1033:       /// This function runs the algorithm.
kpeter@1033:       ///
kpeter@1033:       /// \return The total cost of the found tour.
f4c3@1031:       Cost run() {
f4c3@1031:         _path.clear();
kpeter@1034:         if (_gr.nodeNum() == 0) {
kpeter@1034:           return _sum = 0;
kpeter@1034:         }
kpeter@1033:         else if (_gr.nodeNum() == 1) {
kpeter@1033:           _path.push_back(_gr(0));
kpeter@1033:           return _sum = 0;
kpeter@1033:         }
kpeter@1033: 
kpeter@1034:         std::deque<Node> path_dq;
f4c3@1031:         Edge min_edge1 = INVALID,
f4c3@1031:              min_edge2 = INVALID;
kpeter@1033: 
f4c3@1031:         min_edge1 = mapMin(_gr, _cost);
kpeter@1033:         Node n1 = _gr.u(min_edge1),
f4c3@1031:              n2 = _gr.v(min_edge1);
kpeter@1034:         path_dq.push_back(n1);
kpeter@1034:         path_dq.push_back(n2);
f4c3@1031: 
kpeter@1033:         FullGraph::NodeMap<bool> used(_gr, false);
f4c3@1031:         used[n1] = true;
f4c3@1031:         used[n2] = true;
f4c3@1031: 
f4c3@1031:         min_edge1 = INVALID;
kpeter@1034:         while (int(path_dq.size()) != _gr.nodeNum()) {
f4c3@1031:           if (min_edge1 == INVALID) {
kpeter@1033:             for (IncEdgeIt e(_gr, n1); e != INVALID; ++e) {
kpeter@1033:               if (!used[_gr.runningNode(e)] &&
kpeter@1033:                   (_cost[e] < _cost[min_edge1] || min_edge1 == INVALID)) {
kpeter@1033:                 min_edge1 = e;
f4c3@1031:               }
f4c3@1031:             }
f4c3@1031:           }
f4c3@1031: 
f4c3@1031:           if (min_edge2 == INVALID) {
kpeter@1033:             for (IncEdgeIt e(_gr, n2); e != INVALID; ++e) {
kpeter@1033:               if (!used[_gr.runningNode(e)] &&
kpeter@1033:                   (_cost[e] < _cost[min_edge2] || min_edge2 == INVALID)) {
kpeter@1033:                 min_edge2 = e;
f4c3@1031:               }
f4c3@1031:             }
f4c3@1031:           }
f4c3@1031: 
kpeter@1033:           if (_cost[min_edge1] < _cost[min_edge2]) {
kpeter@1033:             n1 = _gr.oppositeNode(n1, min_edge1);
kpeter@1034:             path_dq.push_front(n1);
f4c3@1031: 
f4c3@1031:             used[n1] = true;
f4c3@1031:             min_edge1 = INVALID;
f4c3@1031: 
kpeter@1033:             if (_gr.u(min_edge2) == n1 || _gr.v(min_edge2) == n1)
f4c3@1031:               min_edge2 = INVALID;
f4c3@1031:           } else {
kpeter@1033:             n2 = _gr.oppositeNode(n2, min_edge2);
kpeter@1034:             path_dq.push_back(n2);
f4c3@1031: 
f4c3@1031:             used[n2] = true;
f4c3@1031:             min_edge2 = INVALID;
f4c3@1031: 
kpeter@1033:             if (_gr.u(min_edge1) == n2 || _gr.v(min_edge1) == n2)
f4c3@1031:               min_edge1 = INVALID;
f4c3@1031:           }
f4c3@1031:         }
f4c3@1031: 
kpeter@1034:         n1 = path_dq.back();
kpeter@1034:         n2 = path_dq.front();
kpeter@1034:         _path.push_back(n2);
kpeter@1034:         _sum = _cost[_gr.edge(n1, n2)];
kpeter@1034:         for (int i = 1; i < int(path_dq.size()); ++i) {
kpeter@1034:           n1 = n2;
kpeter@1034:           n2 = path_dq[i];
kpeter@1034:           _path.push_back(n2);
kpeter@1034:           _sum += _cost[_gr.edge(n1, n2)];
kpeter@1033:         }
f4c3@1031: 
f4c3@1031:         return _sum;
f4c3@1031:       }
f4c3@1031: 
kpeter@1033:       /// @}
kpeter@1033: 
kpeter@1033:       /// \name Query Functions
kpeter@1033:       /// @{
kpeter@1033: 
kpeter@1033:       /// \brief The total cost of the found tour.
kpeter@1033:       ///
kpeter@1033:       /// This function returns the total cost of the found tour.
kpeter@1033:       ///
kpeter@1033:       /// \pre run() must be called before using this function.
kpeter@1033:       Cost tourCost() const {
kpeter@1033:         return _sum;
f4c3@1031:       }
f4c3@1031: 
kpeter@1033:       /// \brief Returns a const reference to the node sequence of the
kpeter@1033:       /// found tour.
kpeter@1033:       ///
kpeter@1034:       /// This function returns a const reference to a vector
kpeter@1033:       /// that stores the node sequence of the found tour.
kpeter@1033:       ///
kpeter@1033:       /// \pre run() must be called before using this function.
kpeter@1034:       const std::vector<Node>& tourNodes() const {
f4c3@1031:         return _path;
f4c3@1031:       }
kpeter@1033: 
kpeter@1033:       /// \brief Gives back the node sequence of the found tour.
kpeter@1033:       ///
kpeter@1033:       /// This function copies the node sequence of the found tour into
kpeter@1037:       /// an STL container through the given output iterator. The
kpeter@1037:       /// <tt>value_type</tt> of the container must be <tt>FullGraph::Node</tt>.
kpeter@1037:       /// For example,
kpeter@1037:       /// \code
kpeter@1037:       /// std::vector<FullGraph::Node> nodes(countNodes(graph));
kpeter@1037:       /// tsp.tourNodes(nodes.begin());
kpeter@1037:       /// \endcode
kpeter@1037:       /// or
kpeter@1037:       /// \code
kpeter@1037:       /// std::list<FullGraph::Node> nodes;
kpeter@1037:       /// tsp.tourNodes(std::back_inserter(nodes));
kpeter@1037:       /// \endcode
kpeter@1033:       ///
kpeter@1033:       /// \pre run() must be called before using this function.
kpeter@1037:       template <typename Iterator>
kpeter@1037:       void tourNodes(Iterator out) const {
kpeter@1037:         std::copy(_path.begin(), _path.end(), out);
kpeter@1033:       }
kpeter@1033: 
kpeter@1033:       /// \brief Gives back the found tour as a path.
kpeter@1033:       ///
kpeter@1033:       /// This function copies the found tour as a list of arcs/edges into
alpar@1074:       /// the given \ref lemon::concepts::Path "path structure".
kpeter@1033:       ///
kpeter@1033:       /// \pre run() must be called before using this function.
kpeter@1033:       template <typename Path>
kpeter@1033:       void tour(Path &path) const {
kpeter@1033:         path.clear();
kpeter@1033:         for (int i = 0; i < int(_path.size()) - 1; ++i) {
kpeter@1033:           path.addBack(_gr.arc(_path[i], _path[i+1]));
f4c3@1031:         }
kpeter@1033:         if (int(_path.size()) >= 2) {
kpeter@1033:           path.addBack(_gr.arc(_path.back(), _path.front()));
kpeter@1033:         }
f4c3@1031:       }
f4c3@1031: 
kpeter@1033:       /// @}
kpeter@1033: 
f4c3@1031:   };
f4c3@1031: 
f4c3@1031: }; // namespace lemon
f4c3@1031: 
f4c3@1031: #endif