We show that the VC-dimension of a graph can be computed in time nlogd+1dO(d), where d is the degeneracy of the input graph. The core idea
of our algorithm is a data structure to efficiently query the number of
vertices that see a specific subset of vertices inside of a (small) query set.
The construction of this data structure takes time O(d2dn), afterwards
queries can be computed efficiently using fast M\"obius inversion.
This data structure turns out to be useful for a range of tasks, especially
for finding bipartite patterns in degenerate graphs, and we outline an
efficient algorithms for counting the number of times specific patterns occur
in a graph. The largest factor in the running time of this algorithm is
O(nc), where c is a parameter of the pattern we call its left covering
number.
Concrete applications of this algorithm include counting the number of
(non-induced) bicliques in linear time, the number of co-matchings in quadratic
time, as well as a constant-factor approximation of the ladder index in linear
time.
Finally, we supplement our theoretical results with several implementations
and run experiments on more than 200 real-world datasets -- the largest of
which has 8 million edges -- where we obtain interesting insights into the
VC-dimension of real-world networks.Comment: Accepted for publication in the 18th International Symposium on
Parameterized and Exact Computation (IPEC 2023