Changeset 1201:9a51db038228 in lemon for lemon/greedy_tsp.h

Timestamp:

01/08/11 22:51:16 (13 years ago)

Author:

Peter Kovacs <kpeter@…>

Branch:

default

Phase:

public

Message:

Document and greatly improve TSP algorithms (#386)

• Add LEMON headers.
• Add Doxygen doc for all classes and their members.
• Clarify and unify the public API of the algorithms.
• Various small improvements in the implementations to make them clearer and faster.
• Avoid using adaptors in ChristofidesTsp?.

File:

• lemon/greedy_tsp.h (modified) (2 diffs)

lemon/greedy_tsp.h

@@ +1 @@
+/* -*- mode: C++; indent-tabs-mode: nil; -*-
+ *
+ * This file is a part of LEMON, a generic C++ optimization library.
+ *
+ * Copyright (C) 2003-2010
+ * 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
 
-#include <lemon/path.h>
+/// \ingroup tsp
+/// \file
+/// \brief Greedy algorithm for symmetric TSP
+
+#include <vector>
+#include <algorithm>
 #include <lemon/full_graph.h>
 #include <lemon/unionfind.h>
-#include <algorithm>
 
 namespace lemon {
 
-  namespace greedy_tsp_helper {
-
-    template <typename CostMap>
-    class KeyComp {
-      typedef typename CostMap::Key Key;
-      const CostMap &cost;
+  /// \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>log(n)) time.
+  /// It quickly finds an effectively short tour for most TSP
+  /// instances, but in special cases, it could yield a really bad
+  /// (or even the worst) solution.
+  ///
+  /// \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:
-        KeyComp(const CostMap &_cost) : cost(_cost) {}
-      
-        bool operator() (const Key &a, const Key &b) const {
-          return cost[a] < cost[b];
-        }
-    };
-
-  
-    template <class L>
-    L vectorConvert(const std::vector<FullGraph::Node> &_path) {
-      return L(_path.begin(), _path.end());
-    }
-  
-    template <>
-    std::vector<FullGraph::Node> vectorConvert(const std::vector<FullGraph::Node> &_path) {
-      return _path;
-    }
-    
-  }
-
-
-  template <typename CM>
-  class GreedyTsp {
-    private:
-      GRAPH_TYPEDEFS(FullGraph);
-    
+        EdgeComp(const CostMap &cost) : _cost(cost) {}
+
+        bool operator()(const Edge &a, const Edge &b) const {
+          return _cost[a] < _cost[b];
+        }
+      };
+
     public:
-      typedef CM CostMap;
-      typedef typename CM::Value Cost;
-      
-      GreedyTsp(const FullGraph &gr, const CostMap &cost) : _gr(gr), _cost(cost) {}  
-
+
+      /// \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() {
-        typedef UnionFind<FullGraph::NodeMap<int> > Union;
-        _nodes.clear();
-        
-        std::vector<int> path;
-        path.resize(_gr.nodeNum()*2, -1);
-        
-        std::vector<typename CostMap::Key> sorted_edges;
+        _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 n(_gr); n != INVALID; ++n)
-          sorted_edges.push_back(n);
-
-        std::sort(sorted_edges.begin(), sorted_edges.end(), greedy_tsp_helper::KeyComp<CostMap>(_cost));
-
-        FullGraph::NodeMap<int> nodemap(_gr);
-        Union unionfind(nodemap);
-
+        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)
-          unionfind.insert(n);
-        
+          union_find.insert(n);
+
         FullGraph::NodeMap<int> degree(_gr, 0);
 
         int nodesNum = 0, i = 0;
-
-        while ( nodesNum != _gr.nodeNum()-1 ) {
-          const Edge &e = sorted_edges[i];
-          
-          const Node u = _gr.u(e),
-                     v = _gr.v(e);
-          
-          if (degree[u]<=1 && degree[v]<=1) {
-            if (unionfind.join(u, v)) {
+        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;
-              
-              const int uid = _gr.id(u),
-                        vid = _gr.id(v);
-              
-              
-              path[uid*2 + (path[uid*2]==-1 ? 0 : 1)] = vid;
-              path[vid*2 + (path[vid*2]==-1 ? 0 : 1)] = uid;
             }
           }
-
-          ++i;
-        }
-
+        }
 
         for (int i=0, n=-1; i<_gr.nodeNum()*2; ++i) {
-          if (path[i] == -1) {
+          if (plist[i] == -1) {
             if (n==-1) {
               n = i;
             } else {
-              path[n] = i/2;
-              path[i] = n/2;
+              plist[n] = i/2;
+              plist[i] = n/2;
               break;
             }
@@ -110 +158 @@
         }
 
-
-        for (int i=0, j=0, last=-1; i!=_gr.nodeNum(); ++i) {
-          _nodes.push_back(_gr.nodeFromId(j));
-          
-          if (path[2*j] != last) {
-            last = j;
-            j = path[2*j];
+        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 = j;
-            j = path[2*j+1];
+            last = next;
+            next = plist[2*next+1];
           }
         }
 
-        _sum = _cost[_gr.edge(_nodes.back(), _nodes.front())];
-        for (unsigned int i=0; i<_nodes.size()-1; ++i)
-          _sum += _cost[_gr.edge(_nodes[i], _nodes[i+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;
       }
 
-
-
-      template <typename L>
-      void tourNodes(L &container) {
-        container(greedy_tsp_helper::vectorConvert<L>(_nodes));
-      }
-      
-      template <template <typename> class L>
-      L<Node> tourNodes() {
-        return greedy_tsp_helper::vectorConvert<L<Node> >(_nodes);
-      }
-      
-      const std::vector<Node>& tourNodes() {
-        return _nodes;
-      }
-      
-      Path<FullGraph> tour() {
-        Path<FullGraph> p;
-        if (_nodes.size()<2)
-          return p;
-        
-        for (unsigned int i=0; i<_nodes.size()-1; ++i) {
-          p.addBack(_gr.arc(_nodes[i], _nodes[i+1]));
-        }
-        
-        p.addBack(_gr.arc(_nodes.back(), _nodes.front()));
-        
-        return p;
-      }
-      
-      Cost tourCost() {
+      /// @}
+
+      /// \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;
       }
-      
-
-    private:
-      const FullGraph &_gr;
-      const CostMap &_cost;
-      Cost _sum;
-      std::vector<Node> _nodes;
+
+      /// \brief Returns a const reference to the node sequence of the
+      /// found tour.
+      ///
+      /// This function returns a const reference to the internal structure
+      /// 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
+      /// the given standard container.
+      ///
+      /// \pre run() must be called before using this function.
+      template <typename Container>
+      void tourNodes(Container &container) const {
+        container.assign(_path.begin(), _path.end());
+      }
+
+      /// \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 concept::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()));
+        }
+      }
+
+      /// @}
+
   };