1 //=======================================================================
2 // Copyright 2001 Jeremy G. Siek, Andrew Lumsdaine, Lie-Quan Lee,
3 //
4 // Distributed under the Boost Software License, Version 1.0. (See
5 // accompanying file LICENSE_1_0.txt or copy at
6 // http://www.boost.org/LICENSE_1_0.txt)
7 //=======================================================================
8 #include <boost/config.hpp>
9 #include <vector>
10 #include <iostream>
11 #include <fstream>
12 #include <iomanip>
13 #include <boost/graph/adjacency_list.hpp>
14 #include <boost/graph/bellman_ford_shortest_paths.hpp>
15
16 using namespace boost;
17
18 template < typename Graph, typename ParentMap > struct edge_writer
19 {
edge_writeredge_writer20 edge_writer(const Graph& g, const ParentMap& p) : m_g(g), m_parent(p) {}
21
22 template < typename Edge >
operator ()edge_writer23 void operator()(std::ostream& out, const Edge& e) const
24 {
25 out << "[label=\"" << get(edge_weight, m_g, e) << "\"";
26 typename graph_traits< Graph >::vertex_descriptor u = source(e, m_g),
27 v = target(e, m_g);
28 if (m_parent[v] == u)
29 out << ", color=\"black\"";
30 else
31 out << ", color=\"grey\"";
32 out << "]";
33 }
34 const Graph& m_g;
35 ParentMap m_parent;
36 };
37 template < typename Graph, typename Parent >
make_edge_writer(const Graph & g,const Parent & p)38 edge_writer< Graph, Parent > make_edge_writer(const Graph& g, const Parent& p)
39 {
40 return edge_writer< Graph, Parent >(g, p);
41 }
42
43 struct EdgeProperties
44 {
45 int weight;
46 };
47
main()48 int main()
49 {
50 enum
51 {
52 u,
53 v,
54 x,
55 y,
56 z,
57 N
58 };
59 char name[] = { 'u', 'v', 'x', 'y', 'z' };
60 typedef std::pair< int, int > E;
61 const int n_edges = 10;
62 E edge_array[] = { E(u, y), E(u, x), E(u, v), E(v, u), E(x, y), E(x, v),
63 E(y, v), E(y, z), E(z, u), E(z, x) };
64 int weight[n_edges] = { -4, 8, 5, -2, 9, -3, 7, 2, 6, 7 };
65
66 typedef adjacency_list< vecS, vecS, directedS, no_property, EdgeProperties >
67 Graph;
68 #if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
69 // VC++ can't handle the iterator constructor
70 Graph g(N);
71 for (std::size_t j = 0; j < n_edges; ++j)
72 add_edge(edge_array[j].first, edge_array[j].second, g);
73 #else
74 Graph g(edge_array, edge_array + n_edges, N);
75 #endif
76 graph_traits< Graph >::edge_iterator ei, ei_end;
77 property_map< Graph, int EdgeProperties::* >::type weight_pmap
78 = get(&EdgeProperties::weight, g);
79 int i = 0;
80 for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei, ++i)
81 weight_pmap[*ei] = weight[i];
82
83 std::vector< int > distance(N, (std::numeric_limits< short >::max)());
84 std::vector< std::size_t > parent(N);
85 for (i = 0; i < N; ++i)
86 parent[i] = i;
87 distance[z] = 0;
88
89 #if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
90 bool r = bellman_ford_shortest_paths(g, int(N), weight_pmap, &parent[0],
91 &distance[0], closed_plus< int >(), std::less< int >(),
92 default_bellman_visitor());
93 #else
94 bool r = bellman_ford_shortest_paths(g, int(N),
95 weight_map(weight_pmap)
96 .distance_map(&distance[0])
97 .predecessor_map(&parent[0]));
98 #endif
99
100 if (r)
101 for (i = 0; i < N; ++i)
102 std::cout << name[i] << ": " << std::setw(3) << distance[i] << " "
103 << name[parent[i]] << std::endl;
104 else
105 std::cout << "negative cycle" << std::endl;
106
107 std::ofstream dot_file("figs/bellman-eg.dot");
108 dot_file << "digraph D {\n"
109 << " rankdir=LR\n"
110 << " size=\"5,3\"\n"
111 << " ratio=\"fill\"\n"
112 << " edge[style=\"bold\"]\n"
113 << " node[shape=\"circle\"]\n";
114
115 {
116 for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei)
117 {
118 graph_traits< Graph >::edge_descriptor e = *ei;
119 graph_traits< Graph >::vertex_descriptor u = source(e, g),
120 v = target(e, g);
121 // VC++ doesn't like the 3-argument get function, so here
122 // we workaround by using 2-nested get()'s.
123 dot_file << name[u] << " -> " << name[v] << "[label=\""
124 << get(get(&EdgeProperties::weight, g), e) << "\"";
125 if (parent[v] == u)
126 dot_file << ", color=\"black\"";
127 else
128 dot_file << ", color=\"grey\"";
129 dot_file << "]";
130 }
131 }
132 dot_file << "}";
133 return EXIT_SUCCESS;
134 }
135