diff -r cd72eae05bdf -r 3c00344f49c9 lemon/opt2_tsp.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lemon/opt2_tsp.h	Wed Oct 17 19:14:07 2018 +0200
@@ -0,0 +1,367 @@
+/* -*- 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_OPT2_TSP_H
+#define LEMON_OPT2_TSP_H
+
+/// \ingroup tsp
+/// \file
+/// \brief 2-opt algorithm for symmetric TSP.
+
+#include <vector>
+#include <lemon/full_graph.h>
+
+namespace lemon {
+
+  /// \ingroup tsp
+  ///
+  /// \brief 2-opt algorithm for symmetric TSP.
+  ///
+  /// Opt2Tsp implements the 2-opt heuristic for solving
+  /// symmetric \ref tsp "TSP".
+  ///
+  /// This algorithm starts with an initial tour and iteratively improves it.
+  /// At each step, it removes two edges and the reconnects the created two
+  /// paths in the other way if the resulting tour is shorter.
+  /// The algorithm finishes when no such 2-opt move can be applied, and so
+  /// the tour is 2-optimal.
+  ///
+  /// If no starting tour is given to the \ref run() function, then the
+  /// algorithm uses the node sequence determined by the node IDs.
+  /// Oherwise, it starts with the given tour.
+  ///
+  /// This is a rather slow but effective method.
+  /// Its typical usage is the improvement of the result of a fast tour
+  /// construction heuristic (e.g. the InsertionTsp algorithm).
+  ///
+  /// \tparam CM Type of the cost map.
+  template <typename CM>
+  class Opt2Tsp
+  {
+    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<int> _plist;
+      std::vector<Node> _path;
+
+    public:
+
+      /// \brief Constructor
+      ///
+      /// Constructor.
+      /// \param gr The \ref FullGraph "full graph" the algorithm runs on.
+      /// \param cost The cost map.
+      Opt2Tsp(const FullGraph &gr, const CostMap &cost)
+        : _gr(gr), _cost(cost) {}
+
+      /// \name Execution Control
+      /// @{
+
+      /// \brief Runs the algorithm from scratch.
+      ///
+      /// This function runs the algorithm starting from the tour that is
+      /// determined by the node ID sequence.
+      ///
+      /// \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;
+        }
+        else if (_gr.nodeNum() == 2) {
+          _path.push_back(_gr(0));
+          _path.push_back(_gr(1));
+          return _sum = 2 * _cost[_gr.edge(_gr(0), _gr(1))];
+        }
+
+        _plist.resize(2*_gr.nodeNum());
+        for (int i = 1; i < _gr.nodeNum()-1; ++i) {
+          _plist[2*i] = i-1;
+          _plist[2*i+1] = i+1;
+        }
+        _plist[0] = _gr.nodeNum()-1;
+        _plist[1] = 1;
+        _plist[2*_gr.nodeNum()-2] = _gr.nodeNum()-2;
+        _plist[2*_gr.nodeNum()-1] = 0;
+
+        return start();
+      }
+
+      /// \brief Runs the algorithm starting from the given tour.
+      ///
+      /// This function runs the algorithm starting from the given tour.
+      ///
+      /// \param tour The tour as a path structure. It must be a
+      /// \ref checkPath() "valid path" containing excactly n arcs.
+      ///
+      /// \return The total cost of the found tour.
+      template <typename Path>
+      Cost run(const Path& tour) {
+        _path.clear();
+
+        if (_gr.nodeNum() == 0) return _sum = 0;
+        else if (_gr.nodeNum() == 1) {
+          _path.push_back(_gr(0));
+          return _sum = 0;
+        }
+        else if (_gr.nodeNum() == 2) {
+          _path.push_back(_gr(0));
+          _path.push_back(_gr(1));
+          return _sum = 2 * _cost[_gr.edge(_gr(0), _gr(1))];
+        }
+
+        _plist.resize(2*_gr.nodeNum());
+        typename Path::ArcIt it(tour);
+        int first = _gr.id(_gr.source(it)),
+            prev = first,
+            curr = _gr.id(_gr.target(it)),
+            next = -1;
+        _plist[2*first+1] = curr;
+        for (++it; it != INVALID; ++it) {
+          next = _gr.id(_gr.target(it));
+          _plist[2*curr] = prev;
+          _plist[2*curr+1] = next;
+          prev = curr;
+          curr = next;
+        }
+        _plist[2*first] = prev;
+
+        return start();
+      }
+
+      /// \brief Runs the algorithm starting from the given tour.
+      ///
+      /// This function runs the algorithm starting from the given tour
+      /// (node sequence).
+      ///
+      /// \param tour A vector that stores all <tt>Node</tt>s of the graph
+      /// in the desired order.
+      ///
+      /// \return The total cost of the found tour.
+      Cost run(const std::vector<Node>& tour) {
+        _path.clear();
+
+        if (_gr.nodeNum() == 0) return _sum = 0;
+        else if (_gr.nodeNum() == 1) {
+          _path.push_back(_gr(0));
+          return _sum = 0;
+        }
+        else if (_gr.nodeNum() == 2) {
+          _path.push_back(_gr(0));
+          _path.push_back(_gr(1));
+          return _sum = 2 * _cost[_gr.edge(_gr(0), _gr(1))];
+        }
+
+        _plist.resize(2*_gr.nodeNum());
+        typename std::vector<Node>::const_iterator it = tour.begin();
+        int first = _gr.id(*it),
+            prev = first,
+            curr = _gr.id(*(++it)),
+            next = -1;
+        _plist[2*first+1] = curr;
+        for (++it; it != tour.end(); ++it) {
+          next = _gr.id(*it);
+          _plist[2*curr] = prev;
+          _plist[2*curr+1] = next;
+          prev = curr;
+          curr = next;
+        }
+        _plist[2*first] = curr;
+        _plist[2*curr] = prev;
+        _plist[2*curr+1] = first;
+
+        return start();
+      }
+
+      /// @}
+
+      /// \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()));
+        }
+      }
+
+      /// @}
+
+    private:
+
+      // Iterator class for the linked list storage of the tour
+      class PathListIt {
+        public:
+          PathListIt(const std::vector<int> &pl, int i=0)
+            : plist(&pl), act(i), last(pl[2*act]) {}
+          PathListIt(const std::vector<int> &pl, int i, int l)
+            : plist(&pl), act(i), last(l) {}
+
+          int nextIndex() const {
+            return (*plist)[2*act] == last ? 2*act+1 : 2*act;
+          }
+
+          int prevIndex() const {
+            return (*plist)[2*act] == last ? 2*act : 2*act+1;
+          }
+
+          int next() const {
+            int x = (*plist)[2*act];
+            return x == last ? (*plist)[2*act+1] : x;
+          }
+
+          int prev() const {
+            return last;
+          }
+
+          PathListIt& operator++() {
+            int tmp = act;
+            act = next();
+            last = tmp;
+            return *this;
+          }
+
+          operator int() const {
+            return act;
+          }
+
+        private:
+          const std::vector<int> *plist;
+          int act;
+          int last;
+      };
+
+      // Checks and applies 2-opt move (if it improves the tour)
+      bool checkOpt2(const PathListIt& i, const PathListIt& j) {
+        Node u  = _gr.nodeFromId(i),
+             un = _gr.nodeFromId(i.next()),
+             v  = _gr.nodeFromId(j),
+             vn = _gr.nodeFromId(j.next());
+
+        if (_cost[_gr.edge(u, un)] + _cost[_gr.edge(v, vn)] >
+            _cost[_gr.edge(u, v)] + _cost[_gr.edge(un, vn)])
+        {
+          _plist[PathListIt(_plist, i.next(), i).prevIndex()] = j.next();
+          _plist[PathListIt(_plist, j.next(), j).prevIndex()] = i.next();
+
+          _plist[i.nextIndex()] = j;
+          _plist[j.nextIndex()] = i;
+
+          return true;
+        }
+
+        return false;
+     }
+
+      // Executes the algorithm from the initial tour
+      Cost start() {
+
+      restart_search:
+        for (PathListIt i(_plist); true; ++i) {
+          PathListIt j = i;
+          if (++j == 0 || ++j == 0) break;
+          for (; j != 0 && j != i.prev(); ++j) {
+            if (checkOpt2(i, j))
+              goto restart_search;
+          }
+        }
+
+        PathListIt i(_plist);
+        _path.push_back(_gr.nodeFromId(i));
+        for (++i; i != 0; ++i)
+          _path.push_back(_gr.nodeFromId(i));
+
+        _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;
+      }
+
+  };
+
+}; // namespace lemon
+
+#endif