diff -r cd72eae05bdf -r 3c00344f49c9 lemon/greedy_tsp.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lemon/greedy_tsp.h	Wed Oct 17 19:14:07 2018 +0200
@@ -0,0 +1,251 @@
+/* -*- 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_GREEDY_TSP_H
+#define LEMON_GREEDY_TSP_H
+
+/// \ingroup tsp
+/// \file
+/// \brief Greedy algorithm for symmetric TSP
+
+#include <vector>
+#include <algorithm>
+#include <lemon/full_graph.h>
+#include <lemon/unionfind.h>
+
+namespace lemon {
+
+  /// \ingroup tsp
+  ///
+  /// \brief Greedy algorithm for symmetric TSP.
+  ///
+  /// GreedyTsp implements the greedy heuristic for solving
+  /// symmetric \ref tsp "TSP".
+  ///
+  /// This algorithm is quite similar to the \ref NearestNeighborTsp
+  /// "nearest neighbor" heuristic, but it maintains a set of disjoint paths.
+  /// At each step, the shortest possible edge is added to these paths
+  /// as long as it does not create a cycle of less than n edges and it does
+  /// not increase the degree of any node above two.
+  ///
+  /// 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 GreedyTsp
+  {
+    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;
+
+    private:
+
+      // Functor class to compare edges by their costs
+      class EdgeComp {
+      private:
+        const CostMap &_cost;
+
+      public:
+        EdgeComp(const CostMap &cost) : _cost(cost) {}
+
+        bool operator()(const Edge &a, const Edge &b) const {
+          return _cost[a] < _cost[b];
+        }
+      };
+
+    public:
+
+      /// \brief Constructor
+      ///
+      /// Constructor.
+      /// \param gr The \ref FullGraph "full graph" the algorithm runs on.
+      /// \param cost The cost map.
+      GreedyTsp(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::vector<int> plist;
+        plist.resize(_gr.nodeNum()*2, -1);
+
+        std::vector<Edge> sorted_edges;
+        sorted_edges.reserve(_gr.edgeNum());
+        for (EdgeIt e(_gr); e != INVALID; ++e)
+          sorted_edges.push_back(e);
+        std::sort(sorted_edges.begin(), sorted_edges.end(), EdgeComp(_cost));
+
+        FullGraph::NodeMap<int> item_int_map(_gr);
+        UnionFind<FullGraph::NodeMap<int> > union_find(item_int_map);
+        for (NodeIt n(_gr); n != INVALID; ++n)
+          union_find.insert(n);
+
+        FullGraph::NodeMap<int> degree(_gr, 0);
+
+        int nodesNum = 0, i = 0;
+        while (nodesNum != _gr.nodeNum()-1) {
+          Edge e = sorted_edges[i++];
+          Node u = _gr.u(e),
+               v = _gr.v(e);
+
+          if (degree[u] <= 1 && degree[v] <= 1) {
+            if (union_find.join(u, v)) {
+              const int uid = _gr.id(u),
+                        vid = _gr.id(v);
+
+              plist[uid*2 + degree[u]] = vid;
+              plist[vid*2 + degree[v]] = uid;
+
+              ++degree[u];
+              ++degree[v];
+              ++nodesNum;
+            }
+          }
+        }
+
+        for (int i=0, n=-1; i<_gr.nodeNum()*2; ++i) {
+          if (plist[i] == -1) {
+            if (n==-1) {
+              n = i;
+            } else {
+              plist[n] = i/2;
+              plist[i] = n/2;
+              break;
+            }
+          }
+        }
+
+        for (int i=0, next=0, last=-1; i!=_gr.nodeNum(); ++i) {
+          _path.push_back(_gr.nodeFromId(next));
+          if (plist[2*next] != last) {
+            last = next;
+            next = plist[2*next];
+          } else {
+            last = next;
+            next = plist[2*next+1];
+          }
+        }
+
+        _sum = _cost[_gr.edge(_path.back(), _path.front())];
+        for (int i = 0; i < int(_path.size())-1; ++i) {
+          _sum += _cost[_gr.edge(_path[i], _path[i+1])];
+        }
+
+        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