COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/work/athos/minlengthpaths.h @ 456:02c28d3cf97b

Last change on this file since 456:02c28d3cf97b was 456:02c28d3cf97b, checked in by Alpar Juttner, 16 years ago

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1// -*- c++ -*-
2#ifndef HUGO_MINLENGTHPATHS_H
3#define HUGO_MINLENGTHPATHS_H
4
5///ingroup galgs
6///\file
7///\brief An algorithm for finding k paths of minimal total length.
8
9#include <iostream>
10#include <dijkstra.h>
11#include <graph_wrapper.h>
12#include <maps.h>
13#include <vector>
14
15
16namespace hugo {
17
18/// \addtogroup galgs
19/// @{
20
21  ///\brief Implementation of an algorithm for finding k paths between 2 nodes
22  /// of minimal total length
23  ///
24  /// The class \ref hugo::MinLengthPaths "MinLengthPaths" implements
25  /// an algorithm which finds k edge-disjoint paths
26  /// from a given source node to a given target node in an
27  /// edge-weighted directed graph having minimal total weigth (length).
28  ///
29  ///\author Attila Bernath
30  template <typename Graph, typename LengthMap>
31  class MinLengthPaths {
32
33    typedef typename LengthMap::ValueType Length;
34
35    typedef typename Graph::Node Node;
36    typedef typename Graph::NodeIt NodeIt;
37    typedef typename Graph::Edge Edge;
38    typedef typename Graph::OutEdgeIt OutEdgeIt;
39    typedef typename Graph::EdgeMap<int> EdgeIntMap;
40
41    typedef ConstMap<Edge,int> ConstMap;
42
43    typedef ResGraphWrapper<const Graph,int,ConstMap,EdgeIntMap> ResGraphType;
44
45
46    class ModLengthMap {   
47      typedef typename ResGraphType::NodeMap<Length> NodeMap;
48      const ResGraphType& G;
49      const EdgeIntMap& rev;
50      const LengthMap &ol;
51      const NodeMap &pot;
52    public :
53      typedef typename LengthMap::KeyType KeyType;
54      typedef typename LengthMap::ValueType ValueType;
55
56      ValueType operator[](typename ResGraphType::Edge e) const {     
57        //if ( (1-2*rev[e])*ol[e]-(pot[G.head(e)]-pot[G.tail(e)] ) <0 ){
58        //  std::cout<<"Negative length!!"<<std::endl;
59        //}
60        return (1-2*rev[e])*ol[e]-(pot[G.head(e)]-pot[G.tail(e)]);   
61      }     
62
63      ModLengthMap(const ResGraphType& _G, const EdgeIntMap& _rev,
64                   const LengthMap &o,  const NodeMap &p) :
65        G(_G), rev(_rev), ol(o), pot(p){};
66    };
67   
68
69    const Graph& G;
70    const LengthMap& length;
71
72    //auxiliary variables
73
74    //The value is 1 iff the edge is reversed.
75    //If the algorithm has finished, the edges of the seeked paths are
76    //exactly those that are reversed
77    EdgeIntMap reversed;
78   
79    //Container to store found paths
80    std::vector< std::vector<Edge> > paths;
81
82  public :
83
84
85    MinLengthPaths(Graph& _G, LengthMap& _length) : G(_G),
86      length(_length), reversed(_G)/*, dijkstra_dist(_G)*/{ }
87
88   
89    ///Runs the algorithm.
90
91    ///Runs the algorithm.
92    ///Returns k if there are at least k edge-disjoint paths from s to t.
93    ///Otherwise it returns the number of found edge-disjoint paths from s to t.
94    int run(Node s, Node t, int k) {
95      ConstMap const1map(1);
96
97      //We need a residual graph, in which some of the edges are reversed
98      ResGraphType res_graph(G, const1map, reversed);
99
100      //Initialize the copy of the Dijkstra potential to zero
101      typename ResGraphType::NodeMap<Length> dijkstra_dist(res_graph);
102      ModLengthMap mod_length(res_graph, reversed, length, dijkstra_dist);
103
104      Dijkstra<ResGraphType, ModLengthMap> dijkstra(res_graph, mod_length);
105
106      int i;
107      for (i=0; i<k; ++i){
108        dijkstra.run(s);
109        if (!dijkstra.reached(t)){
110          //There are no k paths from s to t
111          break;
112        };
113       
114        {
115          //We have to copy the potential
116          typename ResGraphType::NodeIt n;
117          for ( res_graph.first(n) ; res_graph.valid(n) ; res_graph.next(n) ) {
118              dijkstra_dist[n] += dijkstra.distMap()[n];
119          }
120        }
121
122
123        //Reversing the sortest path
124        Node n=t;
125        Edge e;
126        while (n!=s){
127          e = dijkstra.pred(n);
128          n = dijkstra.predNode(n);
129          reversed[e] = 1-reversed[e];
130        }
131
132         
133      }
134     
135      //Let's find the paths
136      //We put the paths into vectors (just for now). In the meantime we lose
137      //the information stored in 'reversed'
138      //We suppose the lengths to be positive now.
139      paths.clear();
140      paths.resize(k);
141      for (int j=0; j<i; ++j){
142        Node n=s;
143        OutEdgeIt e;
144
145        while (n!=t){
146
147
148          G.first(e,n);
149         
150          while (!reversed[e]){
151            G.next(e);
152          }
153          n = G.head(e);
154          paths[j].push_back(e);
155          reversed[e] = 1-reversed[e];
156        }
157       
158      }
159
160      return i;
161    }
162
163
164  }; //class MinLengthPaths
165
166  ///@}
167
168} //namespace hugo
169
170#endif //HUGO_MINLENGTHPATHS_H
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