Last change on this file since 242:b255f25ad394 was 242:b255f25ad394, checked in by Alpar Juttner, 16 years ago
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1// -*- C++ -*-
2
3/*
4 *template <Graph, T, Heap=FibHeap, LengthMap=Graph::EdgeMap<T> >
5 *
6 *Constructor:
7 *
8 *Dijkstra(Graph G, LengthMap length)
9 *
10 *
11 *Methods:
12 *
13 *void run(Node s)
14 *
15 *T dist(Node v) : After run(s) was run, it returns the distance from s to v.
16 *   Returns T() if v is not reachable from s.
17 *
18 *Edge pred(Node v) : After run(s) was run, it returns the last
19 *   edge of a shortest s-v path. It is INVALID for s and for
20 *   the nodes not reachable from s.
21 *
22 *bool reached(Node v) : After run(s) was run, it is true iff v is
23 *   reachable from s
24 *
25 */
26
27#ifndef HUGO_DIJKSTRA_H
28#define HUGO_DIJKSTRA_H
29
30///\file
31///\brief Dijkstra algorithm.
32
33#include <fib_heap.h>
34#include <bin_heap.hh>
35#include <invalid.h>
36
37namespace hugo {
38
39  //Alpar: Changed the order of the parameters
40
41  ///%Dijkstra algorithm class.
42
43  ///This class provides an efficient implementation of %Dijkstra algorithm.
44  ///The edge lengths are passed to the algorithm using a
46  ///so it is easy to change it to any kind of length.
47  ///
48  ///The type of the length is determined by the \c ValueType of the length map.
49  ///
50  ///It is also possible to change the underlying priority heap.
51  ///
52  ///\param Graph The graph type the algorithm runs on.
54  ///EdgeMap
55  ///determines the
56  ///lengths of the edges. It is read once for each edge, so the map
57  ///may involve in relatively time consuming process to compute the edge
58  ///length if it is necessary. The default map type is
59  ///\ref GraphSkeleton::EdgeMap "Graph::EdgeMap<int>"
60  ///\param Heap The heap type used by the %Dijkstra
61  ///algorithm. The default
62  ///is using \ref BinHeap "binary heap".
63
64#ifdef DOXYGEN
65  template <typename Graph,
66            typename LengthMap,
67            typename Heap>
68#else
69  template <typename Graph,
70            typename LengthMap=typename Graph::EdgeMap<int>,
71            typename Heap=BinHeap <typename Graph::Node,
72                                   typename LengthMap::ValueType,
73                                   typename Graph::NodeMap<int> > >
74#endif
75  class Dijkstra{
76  public:
77    typedef typename Graph::Node Node;
78    typedef typename Graph::NodeIt NodeIt;
79    typedef typename Graph::Edge Edge;
80    typedef typename Graph::OutEdgeIt OutEdgeIt;
81
82    typedef typename LengthMap::ValueType ValueType;
83    typedef typename Graph::NodeMap<Edge> PredMap;
84    typedef typename Graph::NodeMap<Node> PredNodeMap;
85    typedef typename Graph::NodeMap<ValueType> DistMap;
86
87  private:
88    const Graph& G;
89    const LengthMap& length;
90    PredMap predecessor;
91    //In place of reach:
92    PredNodeMap pred_node;
93    DistMap distance;
94    //I don't like this:
95    //     //FIXME:
96    //     typename Graph::NodeMap<bool> reach;
97    //     //typename Graph::NodeMap<int> reach;
98
99  public :
100
101    /*
102      The distance of the nodes is 0.
103    */
104    Dijkstra(Graph& _G, LengthMap& _length) :
105      G(_G), length(_length), predecessor(_G), pred_node(_G), distance(_G) { }
106
107
108    void run(Node s);
109
110    ///The distance of a node from the source.
111
112    ///Returns the distance of a node from the source.
113    ///\pre \ref run() must be called before using this function.
114    ///\warning If node \c v in unreachable from the source the return value
115    ///of this funcion is undefined.
116    ValueType dist(Node v) const { return distance[v]; }
117    ///Returns the edges of the shortest path tree.
118
119    ///For a node \c v it returns the last edge of the shortest path
120    ///from the source to \c v or INVALID if \c v is unreachable
121    ///from the source.
122    ///\pre \ref run() must be called before using this function.
123    Edge pred(Node v) const { return predecessor[v]; }
124    ///Returns the nodes of the shortest paths.
125
126    ///For a node \c v it returns the last but one node of the shortest path
127    ///from the source to \c v or INVALID if \c v is unreachable
128    ///from the source.
129    ///\pre \ref run() must be called before using this function.
130    Node predNode(Node v) const { return pred_node[v]; }
131
132    ///Returns a reference to the NodeMap of distances.
133
134    ///\pre \ref run() must be called before using this function.
135    ///
136    const DistMap &distMap() const { return distance;}
137    ///Returns a reference to the shortest path tree map.
138
139    ///Returns a reference to the NodeMap of the edges of the
140    ///shortest path tree.
141    ///\pre \ref run() must be called before using this function.
142    const PredMap &predMap() const { return predecessor;}
143    ///Returns a reference to the map of nodes of  shortest paths.
144
145    ///Returns a reference to the NodeMap of the last but one nodes of the
146    ///shortest paths.
147    ///\pre \ref run() must be called before using this function.
148    const PredNodeMap &predNodeMap() const { return pred_node;}
149
150    //    bool reached(Node v) { return reach[v]; }
151
152    ///Checks if a node is reachable from the source.
153
154    ///Returns \c true if \c v is reachable from the source.
155    ///\warning the source node is reported to be unreached!
156    ///\todo Is this what we want?
157    ///\pre \ref run() must be called before using this function.
158    ///
159    bool reached(Node v) { return G.valid(predecessor[v]); }
160
161  };
162
163
164  // **********************************************************************
165  //  IMPLEMENTATIONS
166  // **********************************************************************
167
168  ///Runs %Dijkstra algorithm from node the source.
169
170  ///This method runs the %Dijkstra algorithm from a source node \c s
171  ///in order to
172  ///compute the
173  ///shortest path to each node. The algorithm computes
174  ///- The shortest path tree.
175  ///- The distance of each node from the source.
176  template <typename Graph, typename LengthMap, typename Heap >
177  void Dijkstra<Graph,LengthMap,Heap>::run(Node s) {
178
179    NodeIt u;
180    for ( G.first(u) ; G.valid(u) ; G.next(u) ) {
181      predecessor.set(u,INVALID);
182      pred_node.set(u,INVALID);
183      // If a node is unreacheable, then why should be the dist=0?
184      // distance.set(u,0);
185      //      reach.set(u,false);
186    }
187
188    //We don't need it at all.
189    //     //FIXME:
190    //     typename Graph::NodeMap<bool> scanned(G,false);
191    //     //typename Graph::NodeMap<int> scanned(G,false);
192    typename Graph::NodeMap<int> heap_map(G,-1);
193
194    Heap heap(heap_map);
195
196    heap.push(s,0);
197    //    reach.set(s, true);
198
199      while ( !heap.empty() ) {
200
201        Node v=heap.top();
202        ValueType oldvalue=heap[v];
203        heap.pop();
204        distance.set(v, oldvalue);
205
206        for(OutEdgeIt e(G,v); G.valid(e); G.next(e)) {
208
209          switch(heap.state(w)) {
210          case Heap::PRE_HEAP:
211            //      reach.set(w,true);
212            heap.push(w,oldvalue+length[e]);
213            predecessor.set(w,e);
214            pred_node.set(w,v);
215            break;
216          case Heap::IN_HEAP:
217            if ( oldvalue+length[e] < heap[w] ) {
218              heap.decrease(w, oldvalue+length[e]);
219              predecessor.set(w,e);
220              pred_node.set(w,v);
221            }
222            break;
223          case Heap::POST_HEAP:
224            break;
225          }
226        }
227      }
228  }
229
230} //END OF NAMESPACE HUGO
231
232#endif
233
234
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