COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/include/dijkstra.h @ 373:259ea2d741a2

Last change on this file since 373:259ea2d741a2 was 373:259ea2d741a2, checked in by jacint, 17 years ago

Changes in the documentation.

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1// -*- C++ -*-
2
3#ifndef HUGO_DIJKSTRA_H
4#define HUGO_DIJKSTRA_H
5
6///\file
7///\brief Dijkstra algorithm.
8
9#include <fib_heap.h>
10#include <bin_heap.h>
11#include <invalid.h>
12
13namespace hugo {
14 
15  ///%Dijkstra algorithm class.
16
17  ///This class provides an efficient implementation of %Dijkstra algorithm.
18  ///The edge lengths are passed to the algorithm using a
19  ///\ref ReadMapSkeleton "readable map",
20  ///so it is easy to change it to any kind of length.
21  ///
22  ///The type of the length is determined by the \c ValueType of the length map.
23  ///
24  ///It is also possible to change the underlying priority heap.
25  ///
26  ///\param Graph The graph type the algorithm runs on. 
27  ///\param LengthMap This read-only EdgeMap determines the lengths of
28  ///the edges. It is read once for each edge, so the map may involve
29  ///in relatively time consuming process to compute the edge length
30  ///if it is necessary. The default map type is \ref
31  ///GraphSkeleton::EdgeMap "Graph::EdgeMap<int>"
32  ///\param Heap The heap type used by the %Dijkstra algorithm. The
33  ///default is using \ref BinHeap "binary heap".
34 
35#ifdef DOXYGEN
36  template <typename Graph,
37            typename LengthMap,
38            typename Heap>
39#else
40  template <typename Graph,
41            typename LengthMap=typename Graph::EdgeMap<int>,
42            template <class,class,class> class Heap = BinHeap >
43#endif
44  class Dijkstra{
45  public:
46    typedef typename Graph::Node Node;
47    typedef typename Graph::NodeIt NodeIt;
48    typedef typename Graph::Edge Edge;
49    typedef typename Graph::OutEdgeIt OutEdgeIt;
50   
51    typedef typename LengthMap::ValueType ValueType;
52    typedef typename Graph::NodeMap<Edge> PredMap;
53    typedef typename Graph::NodeMap<Node> PredNodeMap;
54    typedef typename Graph::NodeMap<ValueType> DistMap;
55
56  private:
57    const Graph& G;
58    const LengthMap& length;
59    PredMap predecessor;
60    PredNodeMap pred_node;
61    DistMap distance;
62   
63  public :
64   
65    Dijkstra(Graph& _G, LengthMap& _length) :
66      G(_G), length(_length), predecessor(_G), pred_node(_G), distance(_G) { }
67   
68    void run(Node s);
69   
70    ///The distance of a node from the source.
71
72    ///Returns the distance of a node from the source.
73    ///\pre \ref run() must be called before using this function.
74    ///\warning If node \c v in unreachable from the source the return value
75    ///of this funcion is undefined.
76    ValueType dist(Node v) const { return distance[v]; }
77
78    ///Returns the edges of the shortest path tree.
79
80    ///For a node \c v it returns the last edge of the shortest path
81    ///from the source to \c v or INVALID if \c v is unreachable
82    ///from the source.
83    ///\pre \ref run() must be called before using this function.
84    Edge pred(Node v) const { return predecessor[v]; }
85
86    ///Returns the nodes of the shortest paths.
87
88    ///For a node \c v it returns the last but one node of the shortest path
89    ///from the source to \c v or INVALID if \c v is unreachable
90    ///from the source.
91    ///\pre \ref run() must be called before using this function.
92    Node predNode(Node v) const { return pred_node[v]; }
93   
94    ///Returns a reference to the NodeMap of distances.
95
96    ///\pre \ref run() must be called before using this function.
97    ///
98    const DistMap &distMap() const { return distance;}
99   
100    ///Returns a reference to the shortest path tree map.
101
102    ///Returns a reference to the NodeMap of the edges of the
103    ///shortest path tree.
104    ///\pre \ref run() must be called before using this function.
105    const PredMap &predMap() const { return predecessor;}
106   
107    ///Returns a reference to the map of nodes of  shortest paths.
108
109    ///Returns a reference to the NodeMap of the last but one nodes of the
110    ///shortest paths.
111    ///\pre \ref run() must be called before using this function.
112    const PredNodeMap &predNodeMap() const { return pred_node;}
113
114    ///Checks if a node is reachable from the source.
115
116    ///Returns \c true if \c v is reachable from the source.
117    ///\warning the source node is reported to be unreached!
118    ///\todo Is this what we want?
119    ///\pre \ref run() must be called before using this function.
120    bool reached(Node v) { return G.valid(predecessor[v]); }
121   
122  };
123 
124
125  // **********************************************************************
126  //  IMPLEMENTATIONS
127  // **********************************************************************
128
129  ///Runs %Dijkstra algorithm from source node \c s.
130
131  ///This method runs the %Dijkstra algorithm from a source node \c s
132  ///in order to compute the shortest path to each node. The algorithm
133  ///computes - The shortest path tree.  - The distance of each node
134  ///from the source.
135  template <typename Graph, typename LengthMap,
136            template<class,class,class> class Heap >
137  void Dijkstra<Graph,LengthMap,Heap>::run(Node s) {
138   
139    NodeIt u;
140    for ( G.first(u) ; G.valid(u) ; G.next(u) ) {
141      predecessor.set(u,INVALID);
142      pred_node.set(u,INVALID);
143    }
144   
145    typename Graph::NodeMap<int> heap_map(G,-1);
146   
147    Heap<Node,ValueType,typename Graph::NodeMap<int> > heap(heap_map);
148    heap.push(s,0);
149   
150    while ( !heap.empty() ) {
151     
152      Node v=heap.top();
153      ValueType oldvalue=heap[v];
154      heap.pop();
155      distance.set(v, oldvalue);
156       
157      { //FIXME this bracket is for e to be local
158        OutEdgeIt e;
159        for(G.first(e, v); G.valid(e); G.next(e)) {
160          Node w=G.head(e);
161         
162          switch(heap.state(w)) {
163          case heap.PRE_HEAP:
164            heap.push(w,oldvalue+length[e]);
165            predecessor.set(w,e);
166            pred_node.set(w,v);
167            break;
168          case heap.IN_HEAP:
169            if ( oldvalue+length[e] < heap[w] ) {
170              heap.decrease(w, oldvalue+length[e]);
171              predecessor.set(w,e);
172              pred_node.set(w,v);
173            }
174            break;
175          case heap.POST_HEAP:
176            break;
177          }
178        }
179      } //FIXME this bracket
180    }
181  }
182 
183} //END OF NAMESPACE HUGO
184
185#endif
186
187
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