COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/work/athos/minlengthpaths.h @ 430:60e4627e8c74

Last change on this file since 430:60e4627e8c74 was 430:60e4627e8c74, 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  template <typename Graph, typename LengthMap>
30  class MinLengthPaths {
31
32    typedef typename LengthMap::ValueType Length;
33
34    typedef typename Graph::Node Node;
35    typedef typename Graph::NodeIt NodeIt;
36    typedef typename Graph::Edge Edge;
37    typedef typename Graph::OutEdgeIt OutEdgeIt;
38    typedef typename Graph::EdgeMap<int> EdgeIntMap;
39
40    typedef ConstMap<Edge,int> ConstMap;
41
42    typedef ResGraphWrapper<const Graph,int,ConstMap,EdgeIntMap> ResGraphType;
43
44
45    class ModLengthMap {   
46      typedef typename ResGraphType::NodeMap<Length> NodeMap;
47      const ResGraphType& G;
48      const EdgeIntMap& rev;
49      const LengthMap &ol;
50      const NodeMap &pot;
51    public :
52      typedef typename LengthMap::KeyType KeyType;
53      typedef typename LengthMap::ValueType ValueType;
54
55      ValueType operator[](typename ResGraphType::Edge e) const {     
56        //if ( (1-2*rev[e])*ol[e]-(pot[G.head(e)]-pot[G.tail(e)] ) <0 ){
57        //  std::cout<<"Negative length!!"<<std::endl;
58        //}
59        return (1-2*rev[e])*ol[e]-(pot[G.head(e)]-pot[G.tail(e)]);   
60      }     
61
62      ModLengthMap(const ResGraphType& _G, const EdgeIntMap& _rev,
63                   const LengthMap &o,  const NodeMap &p) :
64        G(_G), rev(_rev), ol(o), pot(p){};
65    };
66   
67
68    const Graph& G;
69    const LengthMap& length;
70
71    //auxiliary variables
72
73    //The value is 1 iff the edge is reversed.
74    //If the algorithm has finished, the edges of the seeked paths are
75    //exactly those that are reversed
76    EdgeIntMap reversed;
77   
78    //Container to store found paths
79    std::vector< std::vector<Edge> > paths;
80
81  public :
82
83
84    MinLengthPaths(Graph& _G, LengthMap& _length) : G(_G),
85      length(_length), reversed(_G)/*, dijkstra_dist(_G)*/{ }
86
87   
88    ///Runs the algorithm.
89
90    ///Runs the algorithm.
91    ///Returns k if there are at least k edge-disjoint paths from s to t.
92    ///Otherwise it returns the number of found edge-disjoint paths from s to t.
93    int run(Node s, Node t, int k) {
94      ConstMap const1map(1);
95
96      //We need a residual graph, in which some of the edges are reversed
97      ResGraphType res_graph(G, const1map, reversed);
98
99      //Initialize the copy of the Dijkstra potential to zero
100      typename ResGraphType::NodeMap<Length> dijkstra_dist(res_graph);
101      ModLengthMap mod_length(res_graph, reversed, length, dijkstra_dist);
102
103      Dijkstra<ResGraphType, ModLengthMap> dijkstra(res_graph, mod_length);
104
105      int i;
106      for (i=0; i<k; ++i){
107        dijkstra.run(s);
108        if (!dijkstra.reached(t)){
109          //There are no k paths from s to t
110          break;
111        };
112       
113        {
114          //We have to copy the potential
115          typename ResGraphType::NodeIt n;
116          for ( res_graph.first(n) ; res_graph.valid(n) ; res_graph.next(n) ) {
117              dijkstra_dist[n] += dijkstra.distMap()[n];
118          }
119        }
120
121
122        //Reversing the sortest path
123        Node n=t;
124        Edge e;
125        while (n!=s){
126          e = dijkstra.pred(n);
127          n = dijkstra.predNode(n);
128          reversed[e] = 1-reversed[e];
129        }
130
131         
132      }
133     
134      //Let's find the paths
135      //We put the paths into vectors (just for now). In the meantime we lose
136      //the information stored in 'reversed'
137      //We suppose the lengths to be positive now.
138      paths.clear();
139      paths.resize(k);
140      for (int j=0; j<i; ++j){
141        Node n=s;
142        OutEdgeIt e;
143
144        while (n!=t){
145
146
147          G.first(e,n);
148         
149          while (!reversed[e]){
150            G.next(e);
151          }
152          n = G.head(e);
153          paths[j].push_back(e);
154          reversed[e] = 1-reversed[e];
155        }
156       
157      }
158
159      return i;
160    }
161
162
163  }; //class MinLengthPaths
164
165  ///@}
166
167} //namespace hugo
168
169#endif //HUGO_MINLENGTHPATHS_H
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