COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/lemon/bfs.h @ 1164:80bb73097736

Last change on this file since 1164:80bb73097736 was 1164:80bb73097736, checked in by Alpar Juttner, 15 years ago

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1/* -*- C++ -*-
2 * src/lemon/bfs.h - Part of LEMON, a generic C++ optimization library
3 *
4 * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
5 * (Egervary Combinatorial Optimization Research Group, EGRES).
6 *
7 * Permission to use, modify and distribute this software is granted
8 * provided that this copyright notice appears in all copies. For
9 * precise terms see the accompanying LICENSE file.
10 *
11 * This software is provided "AS IS" with no warranty of any kind,
12 * express or implied, and with no claim as to its suitability for any
13 * purpose.
14 *
15 */
16
17#ifndef LEMON_BFS_H
18#define LEMON_BFS_H
19
20///\ingroup flowalgs
21///\file
22///\brief Bfs algorithm.
23///
24///\todo Revise Manual.
25
26#include <lemon/bin_heap.h>
27#include <lemon/invalid.h>
28#include <lemon/graph_utils.h>
29
30namespace lemon {
31
32/// \addtogroup flowalgs
33/// @{
34
35  ///%BFS algorithm class.
36
37  ///This class provides an efficient implementation of %BFS algorithm.
38  ///\param GR The graph type the algorithm runs on.
39  ///This class does the same as Dijkstra does with constant 1 edge length,
40  ///but it is faster.
41  ///
42  ///\author Alpar Juttner
43
44#ifdef DOXYGEN
45  template <typename GR>
46#else
47  template <typename GR>
48#endif
49  class Bfs{
50  public:
51    ///The type of the underlying graph.
52    typedef GR Graph;
53    ///\e
54    typedef typename Graph::Node Node;
55    ///\e
56    typedef typename Graph::NodeIt NodeIt;
57    ///\e
58    typedef typename Graph::Edge Edge;
59    ///\e
60    typedef typename Graph::OutEdgeIt OutEdgeIt;
61   
62    ///\brief The type of the map that stores the last
63    ///edges of the shortest paths.
64    typedef typename Graph::template NodeMap<Edge> PredMap;
65    ///\brief The type of the map that stores the last but one
66    ///nodes of the shortest paths.
67    typedef typename Graph::template NodeMap<Node> PredNodeMap;
68    ///The type of the map that stores the dists of the nodes.
69    typedef typename Graph::template NodeMap<int> DistMap;
70
71  private:
72    /// Pointer to the underlying graph.
73    const Graph *G;
74    ///Pointer to the map of predecessors edges.
75    PredMap *predecessor;
76    ///Indicates if \ref predecessor is locally allocated (\c true) or not.
77    bool local_predecessor;
78    ///Pointer to the map of predecessors nodes.
79    PredNodeMap *pred_node;
80    ///Indicates if \ref pred_node is locally allocated (\c true) or not.
81    bool local_pred_node;
82    ///Pointer to the map of distances.
83    DistMap *distance;
84    ///Indicates if \ref distance is locally allocated (\c true) or not.
85    bool local_distance;
86
87    ///The source node of the last execution.
88    Node source;
89
90
91    ///Initializes the maps.
92    void init_maps()
93    {
94      if(!predecessor) {
95        local_predecessor = true;
96        predecessor = new PredMap(*G);
97      }
98      if(!pred_node) {
99        local_pred_node = true;
100        pred_node = new PredNodeMap(*G);
101      }
102      if(!distance) {
103        local_distance = true;
104        distance = new DistMap(*G);
105      }
106    }
107   
108  public :   
109    ///Constructor.
110   
111    ///\param _G the graph the algorithm will run on.
112    ///
113    Bfs(const Graph& _G) :
114      G(&_G),
115      predecessor(NULL), local_predecessor(false),
116      pred_node(NULL), local_pred_node(false),
117      distance(NULL), local_distance(false)
118    { }
119   
120    ///Destructor.
121    ~Bfs()
122    {
123      if(local_predecessor) delete predecessor;
124      if(local_pred_node) delete pred_node;
125      if(local_distance) delete distance;
126    }
127
128    ///Sets the map storing the predecessor edges.
129
130    ///Sets the map storing the predecessor edges.
131    ///If you don't use this function before calling \ref run(),
132    ///it will allocate one. The destuctor deallocates this
133    ///automatically allocated map, of course.
134    ///\return <tt> (*this) </tt>
135    Bfs &setPredMap(PredMap &m)
136    {
137      if(local_predecessor) {
138        delete predecessor;
139        local_predecessor=false;
140      }
141      predecessor = &m;
142      return *this;
143    }
144
145    ///Sets the map storing the predecessor nodes.
146
147    ///Sets the map storing the predecessor nodes.
148    ///If you don't use this function before calling \ref run(),
149    ///it will allocate one. The destuctor deallocates this
150    ///automatically allocated map, of course.
151    ///\return <tt> (*this) </tt>
152    Bfs &setPredNodeMap(PredNodeMap &m)
153    {
154      if(local_pred_node) {
155        delete pred_node;
156        local_pred_node=false;
157      }
158      pred_node = &m;
159      return *this;
160    }
161
162    ///Sets the map storing the distances calculated by the algorithm.
163
164    ///Sets the map storing the distances calculated by the algorithm.
165    ///If you don't use this function before calling \ref run(),
166    ///it will allocate one. The destuctor deallocates this
167    ///automatically allocated map, of course.
168    ///\return <tt> (*this) </tt>
169    Bfs &setDistMap(DistMap &m)
170    {
171      if(local_distance) {
172        delete distance;
173        local_distance=false;
174      }
175      distance = &m;
176      return *this;
177    }
178   
179  ///Runs %BFS algorithm from node \c s.
180
181  ///This method runs the %BFS algorithm from a root node \c s
182  ///in order to
183  ///compute a
184  ///shortest path to each node. The algorithm computes
185  ///- The %BFS tree.
186  ///- The distance of each node from the root.
187 
188    void run(Node s) {
189     
190      init_maps();
191     
192      source = s;
193     
194      for ( NodeIt u(*G) ; u!=INVALID ; ++u ) {
195        predecessor->set(u,INVALID);
196        pred_node->set(u,INVALID);
197      }
198     
199      int N = countNodes(*G);
200      std::vector<typename Graph::Node> Q(N);
201      int Qh=0;
202      int Qt=0;
203     
204      Q[Qh++]=source;
205      distance->set(s, 0);
206      do {
207        Node m;
208        Node n=Q[Qt++];
209        int d= (*distance)[n]+1;
210       
211        for(OutEdgeIt e(*G,n);e!=INVALID;++e)
212          if((m=G->target(e))!=s && (*predecessor)[m]==INVALID) {
213            Q[Qh++]=m;
214            predecessor->set(m,e);
215            pred_node->set(m,n);
216            distance->set(m,d);
217          }
218      } while(Qt!=Qh);
219    }
220   
221    ///The distance of a node from the root.
222
223    ///Returns the distance of a node from the root.
224    ///\pre \ref run() must be called before using this function.
225    ///\warning If node \c v in unreachable from the root the return value
226    ///of this funcion is undefined.
227    int dist(Node v) const { return (*distance)[v]; }
228
229    ///Returns the 'previous edge' of the %BFS path tree.
230
231    ///For a node \c v it returns the 'previous edge' of the %BFS tree,
232    ///i.e. it returns the last edge of a shortest path from the root to \c
233    ///v. It is \ref INVALID
234    ///if \c v is unreachable from the root or if \c v=s. The
235    ///%BFS tree used here is equal to the %BFS tree used in
236    ///\ref predNode(Node v).  \pre \ref run() must be called before using
237    ///this function.
238    Edge pred(Node v) const { return (*predecessor)[v]; }
239
240    ///Returns the 'previous node' of the %BFS tree.
241
242    ///For a node \c v it returns the 'previous node' on the %BFS tree,
243    ///i.e. it returns the last but one node from a shortest path from the
244    ///root to \c /v. It is INVALID if \c v is unreachable from the root or if
245    ///\c v=s. The shortest path tree used here is equal to the %BFS
246    ///tree used in \ref pred(Node v).  \pre \ref run() must be called before
247    ///using this function.
248    Node predNode(Node v) const { return (*pred_node)[v]; }
249   
250    ///Returns a reference to the NodeMap of distances.
251   
252    ///Returns a reference to the NodeMap of distances. \pre \ref run() must
253    ///be called before using this function.
254    const DistMap &distMap() const { return *distance;}
255 
256    ///Returns a reference to the %BFS tree map.
257
258    ///Returns a reference to the NodeMap of the edges of the
259    ///%BFS tree.
260    ///\pre \ref run() must be called before using this function.
261    const PredMap &predMap() const { return *predecessor;}
262 
263    ///Returns a reference to the map of last but one nodes of shortest paths.
264
265    ///Returns a reference to the NodeMap of the last but one nodes on the
266    ///%BFS tree.
267    ///\pre \ref run() must be called before using this function.
268    const PredNodeMap &predNodeMap() const { return *pred_node;}
269
270    ///Checks if a node is reachable from the root.
271
272    ///Returns \c true if \c v is reachable from the root.
273    ///\note The root node is reported to be reached!
274    ///
275    ///\pre \ref run() must be called before using this function.
276    ///
277    bool reached(Node v) { return v==source || (*predecessor)[v]!=INVALID; }
278   
279  };
280 
281/// @}
282 
283} //END OF NAMESPACE LEMON
284
285#endif
286
287
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