COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/work/athos/minlengthpaths.h @ 330:7ac0d4e8a31c

Last change on this file since 330:7ac0d4e8a31c was 330:7ac0d4e8a31c, checked in by marci, 16 years ago

In the resgraphwrapper interface, and in the constructor,
the order of FlowMap? and CapacityMap? is changed.

File size: 4.1 KB
Line 
1// -*- c++ -*-
2#ifndef HUGO_MINLENGTHPATHS_H
3#define HUGO_MINLENGTHPATHS_H
4
5///\file
6///\brief An algorithm for finding k paths of minimal total length.
7
8#include <iostream>
9#include <dijkstra.h>
10#include <graph_wrapper.h>
11#include <maps.h>
12#include <vector>
13
14
15namespace hugo {
16
17
18
19  ///\brief Implementation of an algorithm for finding k paths between 2 nodes
20  /// of minimal total length
21  ///
22  /// The class \ref hugo::MinLengthPaths "MinLengthPaths" implements
23  /// an algorithm which finds 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 weigth (length).
26
27  template <typename Graph, typename LengthMap>
28  class MinLengthPaths {
29
30    typedef typename LengthMap::ValueType Length;
31
32    typedef typename Graph::Node Node;
33    typedef typename Graph::NodeIt NodeIt;
34    typedef typename Graph::Edge Edge;
35    typedef typename Graph::OutEdgeIt OutEdgeIt;
36    typedef typename Graph::EdgeMap<int> EdgeIntMap;
37
38    typedef ConstMap<Edge,int> ConstMap;
39
40    typedef ResGraphWrapper<const Graph,int,ConstMap,EdgeIntMap> ResGraphType;
41
42
43    class ModLengthMap {   
44      typedef typename ResGraphType::NodeMap<Length> NodeMap;
45      const ResGraphType& G;
46      const EdgeIntMap& rev;
47      const LengthMap &ol;
48      const NodeMap &pot;
49    public :
50      typedef typename LengthMap::KeyType KeyType;
51      typedef typename LengthMap::ValueType ValueType;
52
53      ValueType operator[](typename ResGraphType::Edge e) const {     
54        //if ( (1-2*rev[e])*ol[e]-(pot[G.head(e)]-pot[G.tail(e)] ) <0 ){
55        //  std::cout<<"Negative length!!"<<std::endl;
56        //}
57        return (1-2*rev[e])*ol[e]-(pot[G.head(e)]-pot[G.tail(e)]);   
58      }     
59
60      ModLengthMap(const ResGraphType& _G, const EdgeIntMap& _rev,
61                   const LengthMap &o,  const NodeMap &p) :
62        G(_G), rev(_rev), ol(o), pot(p){};
63    };
64   
65
66    const Graph& G;
67    const LengthMap& length;
68
69    //auxiliary variables
70
71    //The value is 1 iff the edge is reversed.
72    //If the algorithm has finished, the edges of the seeked paths are
73    //exactly those that are reversed
74    EdgeIntMap reversed;
75   
76    //Container to store found paths
77    std::vector< std::vector<Edge> > paths;
78
79  public :
80
81
82    MinLengthPaths(Graph& _G, LengthMap& _length) : G(_G),
83      length(_length), reversed(_G)/*, dijkstra_dist(_G)*/{ }
84
85   
86    ///Runs the algorithm.
87
88    ///Runs the algorithm.
89    ///Returns k if there are at least k edge-disjoint paths from s to t.
90    ///Otherwise it returns the number of found edge-disjoint paths from s to t.
91    int run(Node s, Node t, int k) {
92      ConstMap const1map(1);
93
94      //We need a residual graph, in which some of the edges are reversed
95      ResGraphType res_graph(G, const1map, reversed);
96
97      //Initialize the copy of the Dijkstra potential to zero
98      typename ResGraphType::NodeMap<Length> dijkstra_dist(res_graph);
99      ModLengthMap mod_length(res_graph, reversed, length, dijkstra_dist);
100
101      Dijkstra<ResGraphType, ModLengthMap> dijkstra(res_graph, mod_length);
102
103      int i;
104      for (i=0; i<k; ++i){
105        dijkstra.run(s);
106        if (!dijkstra.reached(t)){
107          //There are no k paths from s to t
108          break;
109        };
110       
111        {
112          //We have to copy the potential
113          typename ResGraphType::NodeIt n;
114          for ( res_graph.first(n) ; res_graph.valid(n) ; res_graph.next(n) ) {
115              dijkstra_dist[n] += dijkstra.distMap()[n];
116          }
117        }
118
119
120        //Reversing the sortest path
121        Node n=t;
122        Edge e;
123        while (n!=s){
124          e = dijkstra.pred(n);
125          n = dijkstra.predNode(n);
126          reversed[e] = 1-reversed[e];
127        }
128
129         
130      }
131     
132      //Let's find the paths
133      //We put the paths into vectors (just for now). In the meantime we lose
134      //the information stored in 'reversed'
135      //We suppose the lengths to be positive now.
136      paths.clear();
137      paths.resize(k);
138      for (int j=0; j<i; ++j){
139        Node n=s;
140        OutEdgeIt e;
141
142        while (n!=t){
143
144
145          G.first(e,n);
146         
147          while (!reversed[e]){
148            G.next(e);
149          }
150          n = G.head(e);
151          paths[j].push_back(e);
152          reversed[e] = 1-reversed[e];
153        }
154       
155      }
156
157      return i;
158    }
159
160
161  }; //class MinLengthPaths
162
163
164} //namespace hugo
165
166#endif //HUGO_MINLENGTHPATHS_H
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