CLEANING REGULAR GRAPHS WITH BRUSHES

A model for cleaning a graph with brushes was recently introduced. We consider the minimum number of brushes needed to clean d-regular graphs in this model, focusing on the asymptotic number for random d-regular graphs. We use a degree-greedy algorithm to clean a random d-regular graph on n vertices (with dn even) and analyze it using the differential equations method to find the (asymptotic) number of brushes needed to clean a random d-regular graph using this algorithm (for fixed d). We further show that for any d-regular graph on n vertices at most n(d + 1)/4 brushes suffice and prove that, for fixed large d, the minimum number of brushes needed to clean a random d-regular graph on n vertices is asymptotically almost surely n/4 (d + o(d)), thus solving a problem raised in [M. E. Messinger, R. J. Nowakowski, P. Pralat, and N. Wormald, Cleaning random d-regular graphs with brushes using a degree-greedy algorithm, in Combinatorial and Algorithmic Aspects of Networking, Lecture Notes in Comput. Sci. 4852, Springer, Berlin-Heidelberg, 2007, pp. 13-26].