1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
|
/* Copyright (c) 1997-2024
Ewgenij Gawrilow, Michael Joswig, and the polymake team
Technische Universität Berlin, Germany
https://polymake.org
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version: http://www.gnu.org/licenses/gpl.txt.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
--------------------------------------------------------------------------------
*/
#include "polymake/graph/graph_iterators.h"
#include "polymake/graph/bipartite.h"
#include "polymake/graph/connected.h"
#include <cstdlib>
namespace polymake { namespace graph {
class BipartiteColoring {
protected:
std::vector<Int> color;
Int sign;
public:
static const bool visit_all_edges=true;
BipartiteColoring();
template <typename TGraph>
explicit BipartiteColoring(const GenericGraph<TGraph>& G)
: color(G.top().dim(), 0)
, sign(0)
{}
template <typename TGraph>
void clear(const GenericGraph<TGraph>& G)
{
std::fill(color.begin(), color.end(), 0);
sign=0;
}
bool operator()(Int n)
{
color[n]=1;
sign=1;
return true;
}
bool operator()(Int n_from, Int n_to)
{
if (color[n_to]==0) {
sign += color[n_to]=-color[n_from];
return true;
} else if (color[n_to]==color[n_from]) {
throw n_to;
} else {
return false;
}
}
Int get_sign() const { return std::abs(sign); }
Int get_color(Int n) const { return color[n]; }
};
template <typename TGraph>
Int bipartite_sign(const GenericGraph<TGraph,Undirected>& G)
{
Int signature = 0;
for (connected_components_iterator<TGraph> C(G); !C.at_end(); ++C) {
Int this_node=C->front();
BFSiterator<TGraph, VisitorTag<BipartiteColoring> > it(G, this_node);
try {
while (!it.at_end()) ++it;
} catch (Int) {
return -1;
}
signature += it.node_visitor().get_sign();
}
return signature;
}
} }
// Local Variables:
// mode:C++
// c-basic-offset:3
// indent-tabs-mode:nil
// End:
|
