Abstract
A minimum cycle basis of a weighted undirected graph G is a ba-
sis of the cycle space of G such that the total weight of the cycles in
this basis is minimized. If G is a planar graph with non-negative edge
weights, such a basis can be found in O(n2) time and space, where n
is the size of G. We show that this is optimal if an explicit represen-
tation of the basis is required. We then present an O(n3/2 log n) time
and O(n3/2) space algorithm that computes a minimum cycle basis
implicitly. From this result, we obtain an output-sensitive algorithm
that explicitly computes a minimum cycle basis in O(n3/2 log n + C)
time and O(n3/2 + C) space, where C is the total size (number of
edges and vertices) of the cycles in the basis. These bounds reduce
to O(n3/2 log n) and O(n3/2), respectively, when G is unweighted. We
get similar results for the all-pairs min cut problem since it is dual
equivalent to the minimum cycle basis problem for planar graphs.
We also obtain O(n3/2 log n) time and O(n3/2) space algorithms for
finding, respectively, the weight vector and a Gomory-Hu tree of G.
The previous best time and space bound for these two problems was
quadratic. From our Gomory-Hu tree algorithm, we obtain the fol-
lowing result: with O(n3/2 log n) time and O(n3/2) space for prepro-
cessing, the weight of a min cut between any two given vertices of G
can be reported in constant time. Previously, such an oracle required
quadratic time and space for preprocessing. The oracle can also be
extended to report the actual cut in time proportional to its size.
| Originalsprog | Engelsk |
|---|---|
| Sider | 1-47 |
| Antal sider | 47 |
| Status | Udgivet - 2009 |