Variations on Cops and Robbers

  • Authors:
  • Alan Frieze;Michael Krivelevich;Po-Shen Loh

  • Affiliations:
  • Department of mathematical sciences carnegie mellon university pittsburgh, pennsylvania15213;School of mathematical sciences raymond and beverly sackler faculty of exact sciences, tel aviv university tel aviv, 69978, israel;Department of mathematical sciences carnegie mellon university pittsburgh, pennsylvania15213

  • Venue:
  • Journal of Graph Theory
  • Year:
  • 2012

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Abstract

We consider several variants of the classical Cops and Robbers game. We treat the version where the robber can move R≥1 edges at a time, establishing a general upper bound of , where α = 1 + 1/R, thus generalizing the best known upper bound for the classical case R = 1 due to Lu and Peng, and Scott and Sudakov. We also show that in this case, the cop number of an n-vertex graph can be as large as n1 − 1/(R − 2) for finite R≥5, but linear in n if R is infinite. For R = 1, we study the directed graph version of the problem, and show that the cop number of any strongly connected digraph on n vertices is O(n(loglogn)2/logn). Our approach is based on expansion. © 2011 Wiley Periodicals, Inc. J Graph Theory. © 2012 Wiley Periodicals, Inc. (Contract grant sponsor: NSF; Contract grant number: DMS-0753472 (to A. F.); Contract grant sponsor: USA-Israel BSF; Contract grant number: 2006322 (to M. K.); Contract grant sponsor: Israel Science Foundation; Contract grant number: 1063/08 (to M. K.); Contract grant sponsor: Pazy memorial award (to M. K.).)