# source:lemon-0.x/src/hugo/suurballe.h@901:69a8e672acb1

Last change on this file since 901:69a8e672acb1 was 901:69a8e672acb1, checked in by marci, 20 years ago

correction of HUGO_... preproc defines.

File size: 6.0 KB
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1// -*- c++ -*-
2#ifndef HUGO_SUURBALLE_H
3#define HUGO_SUURBALLE_H
4
5///\ingroup flowalgs
6///\file
7///\brief An algorithm for finding k paths of minimal total length.
8
9
10#include <hugo/maps.h>
11#include <vector>
12#include <hugo/min_cost_flow.h>
13
14namespace hugo {
15
17/// @{
18
19  ///\brief Implementation of an algorithm for finding k edge-disjoint paths between 2 nodes
20  /// of minimal total length
21  ///
22  /// The class \ref hugo::Suurballe implements
23  /// an algorithm for finding k edge-disjoint paths
24  /// from a given source node to a given target node in an
25  /// edge-weighted directed graph having minimal total weight (length).
26  ///
27  ///\warning Length values should be nonnegative.
28  ///
29  ///\param Graph The directed graph type the algorithm runs on.
30  ///\param LengthMap The type of the length map (values should be nonnegative).
31  ///
32  ///\note It it questionable if it is correct to call this method after
33  ///%Suurballe for it is just a special case of Edmond's and Karp's algorithm
34  ///for finding minimum cost flows. In fact, this implementation is just
35  ///wraps the MinCostFlow algorithms. The paper of both %Suurballe and
36  ///Edmonds-Karp published in 1972, therefore it is possibly right to
37  ///state that they are
38  ///independent results. Most frequently this special case is referred as
39  ///%Suurballe method in the literature, especially in communication
40  ///network context.
41  ///\author Attila Bernath
42  template <typename Graph, typename LengthMap>
43  class Suurballe{
44
45
46    typedef typename LengthMap::ValueType Length;
47
48    typedef typename Graph::Node Node;
49    typedef typename Graph::NodeIt NodeIt;
50    typedef typename Graph::Edge Edge;
51    typedef typename Graph::OutEdgeIt OutEdgeIt;
52    typedef typename Graph::template EdgeMap<int> EdgeIntMap;
53
54    typedef ConstMap<Edge,int> ConstMap;
55
56    //Input
57    const Graph& G;
58
59    //Auxiliary variables
60    //This is the capacity map for the mincostflow problem
61    ConstMap const1map;
62    //This MinCostFlow instance will actually solve the problem
63    MinCostFlow<Graph, LengthMap, ConstMap> mincost_flow;
64
65    //Container to store found paths
66    std::vector< std::vector<Edge> > paths;
67
68  public :
69
70
71    /// The constructor of the class.
72
73    ///\param _G The directed graph the algorithm runs on.
74    ///\param _length The length (weight or cost) of the edges.
75    Suurballe(Graph& _G, LengthMap& _length) : G(_G),
76      const1map(1), mincost_flow(_G, _length, const1map){}
77
78    ///Runs the algorithm.
79
80    ///Runs the algorithm.
81    ///Returns k if there are at least k edge-disjoint paths from s to t.
82    ///Otherwise it returns the number of found edge-disjoint paths from s to t.
83    ///
84    ///\param s The source node.
85    ///\param t The target node.
86    ///\param k How many paths are we looking for?
87    ///
88    int run(Node s, Node t, int k) {
89
90      int i = mincost_flow.run(s,t,k);
91
92
93      //Let's find the paths
94      //We put the paths into stl vectors (as an inner representation).
95      //In the meantime we lose the information stored in 'reversed'.
96      //We suppose the lengths to be positive now.
97
98      //We don't want to change the flow of mincost_flow, so we make a copy
99      //The name here suggests that the flow has only 0/1 values.
100      EdgeIntMap reversed(G);
101
102      for(typename Graph::EdgeIt e(G); e!=INVALID; ++e)
103        reversed[e] = mincost_flow.getFlow()[e];
104
105      paths.clear();
106      //total_length=0;
107      paths.resize(k);
108      for (int j=0; j<i; ++j){
109        Node n=s;
110        OutEdgeIt e;
111
112        while (n!=t){
113
114
115          G.first(e,n);
116
117          while (!reversed[e]){
118            ++e;
119          }
120          n = G.head(e);
121          paths[j].push_back(e);
122          //total_length += length[e];
123          reversed[e] = 1-reversed[e];
124        }
125
126      }
127      return i;
128    }
129
130
131    ///Returns the total length of the paths
132
133    ///This function gives back the total length of the found paths.
134    ///\pre \ref run() must
135    ///be called before using this function.
136    Length totalLength(){
137      return mincost_flow.totalLength();
138    }
139
140    ///Returns the found flow.
141
142    ///This function returns a const reference to the EdgeMap \c flow.
143    ///\pre \ref run() must
144    ///be called before using this function.
145    const EdgeIntMap &getFlow() const { return mincost_flow.flow;}
146
147    /// Returns the optimal dual solution
148
149    ///This function returns a const reference to the NodeMap
150    ///\c potential (the dual solution).
151    /// \pre \ref run() must be called before using this function.
152    const EdgeIntMap &getPotential() const { return mincost_flow.potential;}
153
154    ///Checks whether the complementary slackness holds.
155
156    ///This function checks, whether the given solution is optimal.
157    ///It should return true after calling \ref run()
158    ///Currently this function only checks optimality,
159    ///doesn't bother with feasibility
160    ///It is meant for testing purposes.
161    ///
162    bool checkComplementarySlackness(){
163      return mincost_flow.checkComplementarySlackness();
164    }
165
166    ///Read the found paths.
167
168    ///This function gives back the \c j-th path in argument p.
169    ///Assumes that \c run() has been run and nothing changed since then.
170    /// \warning It is assumed that \c p is constructed to
171    ///be a path of graph \c G.
172    ///If \c j is not less than the result of previous \c run,
173    ///then the result here will be an empty path (\c j can be 0 as well).
174    ///
175    ///\param Path The type of the path structure to put the result to (must meet hugo path concept).
176    ///\param p The path to put the result to
177    ///\param j Which path you want to get from the found paths (in a real application you would get the found paths iteratively)
178    template<typename Path>
179    void getPath(Path& p, size_t j){
180
181      p.clear();
182      if (j>paths.size()-1){
183        return;
184      }
185      typename Path::Builder B(p);
186      for(typename std::vector<Edge>::iterator i=paths[j].begin();
187          i!=paths[j].end(); ++i ){
188        B.pushBack(*i);
189      }
190
191      B.commit();
192    }
193
194  }; //class Suurballe
195
196  ///@}
197
198} //namespace hugo
199
200#endif //HUGO_SUURBALLE_H
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