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 <hugo/dijkstra.h> |
---|
11 | //#include <hugo/graph_wrapper.h> |
---|
12 | #include <hugo/maps.h> |
---|
13 | #include <vector> |
---|
14 | #include <mincostflows.h> |
---|
15 | #include <for_each_macros.h> |
---|
16 | |
---|
17 | namespace hugo { |
---|
18 | |
---|
19 | /// \addtogroup galgs |
---|
20 | /// @{ |
---|
21 | |
---|
22 | ///\brief Implementation of an algorithm for finding k paths between 2 nodes |
---|
23 | /// of minimal total length |
---|
24 | /// |
---|
25 | /// The class \ref hugo::MinLengthPaths "MinLengthPaths" implements |
---|
26 | /// an algorithm for finding k edge-disjoint paths |
---|
27 | /// from a given source node to a given target node in an |
---|
28 | /// edge-weighted directed graph having minimal total weigth (length). |
---|
29 | /// |
---|
30 | ///\warning It is assumed that the lengths are positive, since the |
---|
31 | /// general flow-decomposition is not implemented yet. |
---|
32 | /// |
---|
33 | ///\author Attila Bernath |
---|
34 | template <typename Graph, typename LengthMap> |
---|
35 | class MinLengthPaths{ |
---|
36 | |
---|
37 | |
---|
38 | typedef typename LengthMap::ValueType Length; |
---|
39 | |
---|
40 | typedef typename Graph::Node Node; |
---|
41 | typedef typename Graph::NodeIt NodeIt; |
---|
42 | typedef typename Graph::Edge Edge; |
---|
43 | typedef typename Graph::OutEdgeIt OutEdgeIt; |
---|
44 | typedef typename Graph::template EdgeMap<int> EdgeIntMap; |
---|
45 | |
---|
46 | typedef ConstMap<Edge,int> ConstMap; |
---|
47 | |
---|
48 | //Input |
---|
49 | const Graph& G; |
---|
50 | |
---|
51 | //Auxiliary variables |
---|
52 | //This is the capacity map for the mincostflow problem |
---|
53 | ConstMap const1map; |
---|
54 | //This MinCostFlows instance will actually solve the problem |
---|
55 | MinCostFlows<Graph, LengthMap, ConstMap> mincost_flow; |
---|
56 | |
---|
57 | //Container to store found paths |
---|
58 | std::vector< std::vector<Edge> > paths; |
---|
59 | |
---|
60 | public : |
---|
61 | |
---|
62 | |
---|
63 | MinLengthPaths(Graph& _G, LengthMap& _length) : G(_G), |
---|
64 | const1map(1), mincost_flow(_G, _length, const1map){} |
---|
65 | |
---|
66 | ///Runs the algorithm. |
---|
67 | |
---|
68 | ///Runs the algorithm. |
---|
69 | ///Returns k if there are at least k edge-disjoint paths from s to t. |
---|
70 | ///Otherwise it returns the number of found edge-disjoint paths from s to t. |
---|
71 | int run(Node s, Node t, int k) { |
---|
72 | |
---|
73 | int i = mincost_flow.run(s,t,k); |
---|
74 | |
---|
75 | |
---|
76 | |
---|
77 | //Let's find the paths |
---|
78 | //We put the paths into stl vectors (as an inner representation). |
---|
79 | //In the meantime we lose the information stored in 'reversed'. |
---|
80 | //We suppose the lengths to be positive now. |
---|
81 | |
---|
82 | //We don't want to change the flow of mincost_flow, so we make a copy |
---|
83 | //The name here suggests that the flow has only 0/1 values. |
---|
84 | EdgeIntMap reversed(G); |
---|
85 | |
---|
86 | FOR_EACH_LOC(typename Graph::EdgeIt, e, G){ |
---|
87 | reversed[e] = mincost_flow.getFlow()[e]; |
---|
88 | } |
---|
89 | |
---|
90 | paths.clear(); |
---|
91 | //total_length=0; |
---|
92 | paths.resize(k); |
---|
93 | for (int j=0; j<i; ++j){ |
---|
94 | Node n=s; |
---|
95 | OutEdgeIt e; |
---|
96 | |
---|
97 | while (n!=t){ |
---|
98 | |
---|
99 | |
---|
100 | G.first(e,n); |
---|
101 | |
---|
102 | while (!reversed[e]){ |
---|
103 | G.next(e); |
---|
104 | } |
---|
105 | n = G.head(e); |
---|
106 | paths[j].push_back(e); |
---|
107 | //total_length += length[e]; |
---|
108 | reversed[e] = 1-reversed[e]; |
---|
109 | } |
---|
110 | |
---|
111 | } |
---|
112 | return i; |
---|
113 | } |
---|
114 | |
---|
115 | |
---|
116 | ///This function gives back the total length of the found paths. |
---|
117 | ///Assumes that \c run() has been run and nothing changed since then. |
---|
118 | Length totalLength(){ |
---|
119 | return mincost_flow.totalLength(); |
---|
120 | } |
---|
121 | |
---|
122 | ///Returns a const reference to the EdgeMap \c flow. \pre \ref run() must |
---|
123 | ///be called before using this function. |
---|
124 | const EdgeIntMap &getFlow() const { return mincost_flow.flow;} |
---|
125 | |
---|
126 | ///Returns a const reference to the NodeMap \c potential (the dual solution). |
---|
127 | /// \pre \ref run() must be called before using this function. |
---|
128 | const EdgeIntMap &getPotential() const { return mincost_flow.potential;} |
---|
129 | |
---|
130 | ///This function checks, whether the given solution is optimal |
---|
131 | ///Running after a \c run() should return with true |
---|
132 | ///In this "state of the art" this only checks optimality, doesn't bother with feasibility |
---|
133 | /// |
---|
134 | ///\todo Is this OK here? |
---|
135 | bool checkComplementarySlackness(){ |
---|
136 | return mincost_flow.checkComplementarySlackness(); |
---|
137 | } |
---|
138 | |
---|
139 | ///This function gives back the \c j-th path in argument p. |
---|
140 | ///Assumes that \c run() has been run and nothing changed since then. |
---|
141 | /// \warning It is assumed that \c p is constructed to be a path of graph \c G. If \c j is not less than the result of previous \c run, then the result here will be an empty path (\c j can be 0 as well). |
---|
142 | template<typename DirPath> |
---|
143 | void getPath(DirPath& p, size_t j){ |
---|
144 | |
---|
145 | p.clear(); |
---|
146 | if (j>paths.size()-1){ |
---|
147 | return; |
---|
148 | } |
---|
149 | typename DirPath::Builder B(p); |
---|
150 | for(typename std::vector<Edge>::iterator i=paths[j].begin(); |
---|
151 | i!=paths[j].end(); ++i ){ |
---|
152 | B.pushBack(*i); |
---|
153 | } |
---|
154 | |
---|
155 | B.commit(); |
---|
156 | } |
---|
157 | |
---|
158 | }; //class MinLengthPaths |
---|
159 | |
---|
160 | ///@} |
---|
161 | |
---|
162 | } //namespace hugo |
---|
163 | |
---|
164 | #endif //HUGO_MINLENGTHPATHS_H |
---|