COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/work/jacint/prim.h @ 986:e997802b855c

Last change on this file since 986:e997802b855c was 986:e997802b855c, checked in by Alpar Juttner, 15 years ago

Naming changes:

  • head -> target
  • tail -> source
File size: 3.3 KB
Line 
1// -*- C++ -*-
2/*
3 *template <Graph, T, Heap=FibHeap, LengthMap=Graph::EdgeMap<T> >
4 *
5 *Constructor:
6 *
7 *Prim(Graph G, LengthMap weight)
8 *
9 *
10 *Methods:
11 *
12 *void run() : Runs the Prim-algorithm from a random node
13 *
14 *void run(Node r) : Runs the Prim-algorithm from node s
15 *
16 *T weight() : After run(r) was run, it returns the minimum
17 *   weight of a spanning tree of the component of the root.
18 *
19 *Edge tree(Node v) : After run(r) was run, it returns the
20 *   first edge in the path from v to the root. Returns
21 *   INVALID if v=r or v is not reachable from the root.
22 *
23 *bool conn() : After run(r) was run, it is true iff G is connected
24 *
25 *bool reached(Node v) : After run(r) was run, it is true
26 *   iff v is in the same component as the root
27 *
28 *Node root() : returns the root
29 *
30 */
31
32#ifndef LEMON_PRIM_H
33#define LEMON_PRIM_H
34
35#include <fib_heap.h>
36#include <invalid.h>
37
38namespace lemon {
39
40  template <typename Graph, typename T,
41    typename Heap=FibHeap<typename Graph::Node, T,
42    typename Graph::NodeMap<int> >,
43    typename LengthMap=typename Graph::EdgeMap<T> >
44    class Prim{
45      typedef typename Graph::Node Node;
46      typedef typename Graph::NodeIt NodeIt;
47      typedef typename Graph::Edge Edge;
48      typedef typename Graph::OutEdgeIt OutEdgeIt;
49      typedef typename Graph::InEdgeIt InEdgeIt; 
50
51      const Graph& G;
52      const LengthMap& edge_weight;
53      typename Graph::NodeMap<Edge> tree_edge;
54      typename Graph::NodeMap<T> min_weight;
55      typename Graph::NodeMap<bool> reach;
56         
57  public :
58
59      Prim(Graph& _G, LengthMap& _edge_weight) :
60        G(_G), edge_weight(_edge_weight),
61        tree_edge(_G,INVALID), min_weight(_G), reach(_G, false) { }
62
63
64      void run() {
65        NodeIt _r;     
66        G.first(_r);
67        run(_r);
68      }
69
70
71      void run(Node r) {
72
73        NodeIt u;
74        for ( G.first(u) ; G.valid(u) ; G.next(u) ) {
75          tree_edge.set(u,INVALID);
76          min_weight.set(u,0);
77          reach.set(u,false);
78        }
79
80
81        typename Graph::NodeMap<bool> scanned(G, false);
82        typename Graph::NodeMap<int> heap_map(G,-1);
83       
84        Heap heap(heap_map);
85
86        heap.push(r,0);
87        reach.set(r, true);
88
89        while ( !heap.empty() ) {
90
91          Node v=heap.top();
92          min_weight.set(v, heap.get(v));
93          heap.pop();
94          scanned.set(v,true);
95
96          OutEdgeIt e;
97          for( G.first(e,v); G.valid(e); G.next(e)) {
98            Node w=G.target(e);
99           
100            if ( !scanned[w] ) {
101              if ( !reach[w] ) {
102                reach.set(w,true);
103                heap.push(w, edge_weight[e]);
104                tree_edge.set(w,e);
105              } else if ( edge_weight[e] < heap.get(w) ) {
106                tree_edge.set(w,e);
107                heap.decrease(w, edge_weight[e]);
108              }
109            }
110          }
111
112          InEdgeIt f;
113          for( G.first(f,v); G.valid(f); G.next(f)) {
114            Node w=G.source(f);
115           
116            if ( !scanned[w] ) {
117              if ( !reach[w] ) {
118                reach.set(w,true);
119                heap.push(w, edge_weight[f]);
120                tree_edge.set(w,f);
121              } else if ( edge_weight[f] < heap.get(w) ) {
122                tree_edge.set(w,f);
123                heap.decrease(w, edge_weight[f]);
124              }
125            }
126          }
127        }
128      }
129 
130
131      T weight() {
132        T w=0;
133        NodeIt u;
134        for ( G.first(u) ; G.valid(u) ; G.next(u) ) w+=min_weight[u];
135        return w;
136      }
137     
138
139      Edge tree(Node v) {
140        return tree_edge[v];
141      }
142
143
144      bool conn() {
145        bool c=true;
146        NodeIt u;
147        for ( G.first(u) ; G.valid(u) ; G.next(u) )
148          if ( !reached[u] ) {
149            c=false;
150            break;
151          }
152        return c;
153      }
154
155
156      bool reached(Node v) {
157        return reached[v];
158      }
159
160
161      Node root() {
162        return r;
163      }
164
165    };
166
167}
168
169#endif
170
171
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