diff -r cd72eae05bdf -r 3c00344f49c9 lemon/nearest_neighbor_tsp.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lemon/nearest_neighbor_tsp.h	Wed Oct 17 19:14:07 2018 +0200
@@ -0,0 +1,238 @@
+/* -*- 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