lemon/kruskal.h
author Peter Kovacs <kpeter@inf.elte.hu>
Sun, 30 Nov 2008 00:48:07 +0100
changeset 392 db3251947eba
parent 216 6d7bfcf5b48e
child 440 88ed40ad0d4f
permissions -rw-r--r--
Rename flowInit() to init() in Preflow (#176)
     1 /* -*- mode: C++; indent-tabs-mode: nil; -*-
     2  *
     3  * This file is a part of LEMON, a generic C++ optimization library.
     4  *
     5  * Copyright (C) 2003-2008
     6  * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
     7  * (Egervary Research Group on Combinatorial Optimization, EGRES).
     8  *
     9  * Permission to use, modify and distribute this software is granted
    10  * provided that this copyright notice appears in all copies. For
    11  * precise terms see the accompanying LICENSE file.
    12  *
    13  * This software is provided "AS IS" with no warranty of any kind,
    14  * express or implied, and with no claim as to its suitability for any
    15  * purpose.
    16  *
    17  */
    18 
    19 #ifndef LEMON_KRUSKAL_H
    20 #define LEMON_KRUSKAL_H
    21 
    22 #include <algorithm>
    23 #include <vector>
    24 #include <lemon/unionfind.h>
    25 #include <lemon/maps.h>
    26 
    27 #include <lemon/core.h>
    28 #include <lemon/bits/traits.h>
    29 
    30 ///\ingroup spantree
    31 ///\file
    32 ///\brief Kruskal's algorithm to compute a minimum cost spanning tree
    33 ///
    34 ///Kruskal's algorithm to compute a minimum cost spanning tree.
    35 ///
    36 
    37 namespace lemon {
    38 
    39   namespace _kruskal_bits {
    40 
    41     // Kruskal for directed graphs.
    42 
    43     template <typename Digraph, typename In, typename Out>
    44     typename disable_if<lemon::UndirectedTagIndicator<Digraph>,
    45                        typename In::value_type::second_type >::type
    46     kruskal(const Digraph& digraph, const In& in, Out& out,dummy<0> = 0) {
    47       typedef typename In::value_type::second_type Value;
    48       typedef typename Digraph::template NodeMap<int> IndexMap;
    49       typedef typename Digraph::Node Node;
    50 
    51       IndexMap index(digraph);
    52       UnionFind<IndexMap> uf(index);
    53       for (typename Digraph::NodeIt it(digraph); it != INVALID; ++it) {
    54         uf.insert(it);
    55       }
    56 
    57       Value tree_value = 0;
    58       for (typename In::const_iterator it = in.begin(); it != in.end(); ++it) {
    59         if (uf.join(digraph.target(it->first),digraph.source(it->first))) {
    60           out.set(it->first, true);
    61           tree_value += it->second;
    62         }
    63         else {
    64           out.set(it->first, false);
    65         }
    66       }
    67       return tree_value;
    68     }
    69 
    70     // Kruskal for undirected graphs.
    71 
    72     template <typename Graph, typename In, typename Out>
    73     typename enable_if<lemon::UndirectedTagIndicator<Graph>,
    74                        typename In::value_type::second_type >::type
    75     kruskal(const Graph& graph, const In& in, Out& out,dummy<1> = 1) {
    76       typedef typename In::value_type::second_type Value;
    77       typedef typename Graph::template NodeMap<int> IndexMap;
    78       typedef typename Graph::Node Node;
    79 
    80       IndexMap index(graph);
    81       UnionFind<IndexMap> uf(index);
    82       for (typename Graph::NodeIt it(graph); it != INVALID; ++it) {
    83         uf.insert(it);
    84       }
    85 
    86       Value tree_value = 0;
    87       for (typename In::const_iterator it = in.begin(); it != in.end(); ++it) {
    88         if (uf.join(graph.u(it->first),graph.v(it->first))) {
    89           out.set(it->first, true);
    90           tree_value += it->second;
    91         }
    92         else {
    93           out.set(it->first, false);
    94         }
    95       }
    96       return tree_value;
    97     }
    98 
    99 
   100     template <typename Sequence>
   101     struct PairComp {
   102       typedef typename Sequence::value_type Value;
   103       bool operator()(const Value& left, const Value& right) {
   104         return left.second < right.second;
   105       }
   106     };
   107 
   108     template <typename In, typename Enable = void>
   109     struct SequenceInputIndicator {
   110       static const bool value = false;
   111     };
   112 
   113     template <typename In>
   114     struct SequenceInputIndicator<In,
   115       typename exists<typename In::value_type::first_type>::type> {
   116       static const bool value = true;
   117     };
   118 
   119     template <typename In, typename Enable = void>
   120     struct MapInputIndicator {
   121       static const bool value = false;
   122     };
   123 
   124     template <typename In>
   125     struct MapInputIndicator<In,
   126       typename exists<typename In::Value>::type> {
   127       static const bool value = true;
   128     };
   129 
   130     template <typename In, typename Enable = void>
   131     struct SequenceOutputIndicator {
   132       static const bool value = false;
   133     };
   134 
   135     template <typename Out>
   136     struct SequenceOutputIndicator<Out,
   137       typename exists<typename Out::value_type>::type> {
   138       static const bool value = true;
   139     };
   140 
   141     template <typename Out, typename Enable = void>
   142     struct MapOutputIndicator {
   143       static const bool value = false;
   144     };
   145 
   146     template <typename Out>
   147     struct MapOutputIndicator<Out,
   148       typename exists<typename Out::Value>::type> {
   149       static const bool value = true;
   150     };
   151 
   152     template <typename In, typename InEnable = void>
   153     struct KruskalValueSelector {};
   154 
   155     template <typename In>
   156     struct KruskalValueSelector<In,
   157       typename enable_if<SequenceInputIndicator<In>, void>::type>
   158     {
   159       typedef typename In::value_type::second_type Value;
   160     };
   161 
   162     template <typename In>
   163     struct KruskalValueSelector<In,
   164       typename enable_if<MapInputIndicator<In>, void>::type>
   165     {
   166       typedef typename In::Value Value;
   167     };
   168 
   169     template <typename Graph, typename In, typename Out,
   170               typename InEnable = void>
   171     struct KruskalInputSelector {};
   172 
   173     template <typename Graph, typename In, typename Out,
   174               typename InEnable = void>
   175     struct KruskalOutputSelector {};
   176 
   177     template <typename Graph, typename In, typename Out>
   178     struct KruskalInputSelector<Graph, In, Out,
   179       typename enable_if<SequenceInputIndicator<In>, void>::type >
   180     {
   181       typedef typename In::value_type::second_type Value;
   182 
   183       static Value kruskal(const Graph& graph, const In& in, Out& out) {
   184         return KruskalOutputSelector<Graph, In, Out>::
   185           kruskal(graph, in, out);
   186       }
   187 
   188     };
   189 
   190     template <typename Graph, typename In, typename Out>
   191     struct KruskalInputSelector<Graph, In, Out,
   192       typename enable_if<MapInputIndicator<In>, void>::type >
   193     {
   194       typedef typename In::Value Value;
   195       static Value kruskal(const Graph& graph, const In& in, Out& out) {
   196         typedef typename In::Key MapArc;
   197         typedef typename In::Value Value;
   198         typedef typename ItemSetTraits<Graph, MapArc>::ItemIt MapArcIt;
   199         typedef std::vector<std::pair<MapArc, Value> > Sequence;
   200         Sequence seq;
   201 
   202         for (MapArcIt it(graph); it != INVALID; ++it) {
   203           seq.push_back(std::make_pair(it, in[it]));
   204         }
   205 
   206         std::sort(seq.begin(), seq.end(), PairComp<Sequence>());
   207         return KruskalOutputSelector<Graph, Sequence, Out>::
   208           kruskal(graph, seq, out);
   209       }
   210     };
   211 
   212     template <typename T>
   213     struct RemoveConst {
   214       typedef T type;
   215     };
   216 
   217     template <typename T>
   218     struct RemoveConst<const T> {
   219       typedef T type;
   220     };
   221 
   222     template <typename Graph, typename In, typename Out>
   223     struct KruskalOutputSelector<Graph, In, Out,
   224       typename enable_if<SequenceOutputIndicator<Out>, void>::type >
   225     {
   226       typedef typename In::value_type::second_type Value;
   227 
   228       static Value kruskal(const Graph& graph, const In& in, Out& out) {
   229         typedef LoggerBoolMap<typename RemoveConst<Out>::type> Map;
   230         Map map(out);
   231         return _kruskal_bits::kruskal(graph, in, map);
   232       }
   233 
   234     };
   235 
   236     template <typename Graph, typename In, typename Out>
   237     struct KruskalOutputSelector<Graph, In, Out,
   238       typename enable_if<MapOutputIndicator<Out>, void>::type >
   239     {
   240       typedef typename In::value_type::second_type Value;
   241 
   242       static Value kruskal(const Graph& graph, const In& in, Out& out) {
   243         return _kruskal_bits::kruskal(graph, in, out);
   244       }
   245     };
   246 
   247   }
   248 
   249   /// \ingroup spantree
   250   ///
   251   /// \brief Kruskal algorithm to find a minimum cost spanning tree of
   252   /// a graph.
   253   ///
   254   /// This function runs Kruskal's algorithm to find a minimum cost
   255   /// spanning tree.
   256   /// Due to some C++ hacking, it accepts various input and output types.
   257   ///
   258   /// \param g The graph the algorithm runs on.
   259   /// It can be either \ref concepts::Digraph "directed" or
   260   /// \ref concepts::Graph "undirected".
   261   /// If the graph is directed, the algorithm consider it to be
   262   /// undirected by disregarding the direction of the arcs.
   263   ///
   264   /// \param in This object is used to describe the arc/edge costs.
   265   /// It can be one of the following choices.
   266   /// - An STL compatible 'Forward Container' with
   267   /// <tt>std::pair<GR::Arc,X></tt> or
   268   /// <tt>std::pair<GR::Edge,X></tt> as its <tt>value_type</tt>, where
   269   /// \c X is the type of the costs. The pairs indicates the arcs/edges
   270   /// along with the assigned cost. <em>They must be in a
   271   /// cost-ascending order.</em>
   272   /// - Any readable arc/edge map. The values of the map indicate the
   273   /// arc/edge costs.
   274   ///
   275   /// \retval out Here we also have a choice.
   276   /// - It can be a writable \c bool arc/edge map. After running the
   277   /// algorithm it will contain the found minimum cost spanning
   278   /// tree: the value of an arc/edge will be set to \c true if it belongs
   279   /// to the tree, otherwise it will be set to \c false. The value of
   280   /// each arc/edge will be set exactly once.
   281   /// - It can also be an iteraror of an STL Container with
   282   /// <tt>GR::Arc</tt> or <tt>GR::Edge</tt> as its
   283   /// <tt>value_type</tt>.  The algorithm copies the elements of the
   284   /// found tree into this sequence.  For example, if we know that the
   285   /// spanning tree of the graph \c g has say 53 arcs, then we can
   286   /// put its arcs into an STL vector \c tree with a code like this.
   287   ///\code
   288   /// std::vector<Arc> tree(53);
   289   /// kruskal(g,cost,tree.begin());
   290   ///\endcode
   291   /// Or if we don't know in advance the size of the tree, we can
   292   /// write this.
   293   ///\code
   294   /// std::vector<Arc> tree;
   295   /// kruskal(g,cost,std::back_inserter(tree));
   296   ///\endcode
   297   ///
   298   /// \return The total cost of the found spanning tree.
   299   ///
   300   /// \note If the input graph is not (weakly) connected, a spanning
   301   /// forest is calculated instead of a spanning tree.
   302 
   303 #ifdef DOXYGEN
   304   template <class Graph, class In, class Out>
   305   Value kruskal(GR const& g, const In& in, Out& out)
   306 #else
   307   template <class Graph, class In, class Out>
   308   inline typename _kruskal_bits::KruskalValueSelector<In>::Value
   309   kruskal(const Graph& graph, const In& in, Out& out)
   310 #endif
   311   {
   312     return _kruskal_bits::KruskalInputSelector<Graph, In, Out>::
   313       kruskal(graph, in, out);
   314   }
   315 
   316 
   317 
   318 
   319   template <class Graph, class In, class Out>
   320   inline typename _kruskal_bits::KruskalValueSelector<In>::Value
   321   kruskal(const Graph& graph, const In& in, const Out& out)
   322   {
   323     return _kruskal_bits::KruskalInputSelector<Graph, In, const Out>::
   324       kruskal(graph, in, out);
   325   }
   326 
   327 } //namespace lemon
   328 
   329 #endif //LEMON_KRUSKAL_H