Online vertex colorings of random graphs without monochromatic subgraphs

  • Authors:
  • Martin Marciniszyn;Reto Spöhel

  • Affiliations:
  • Institute of Theoretical Computer Science, ETH Zurich, Zurich, Switzerland;Institute of Theoretical Computer Science, ETH Zurich, Zurich, Switzerland

  • Venue:
  • SODA '07 Proceedings of the eighteenth annual ACM-SIAM symposium on Discrete algorithms
  • Year:
  • 2007

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Abstract

Consider the following generalized notion of graph colorings: a vertex coloring of graph G is valid w.r.t. some fixed nonempty graph F if no color class induces a copy of F in G, i.e., there is no monochromatic copy of F in G. We propose and analyze an algorithm for computing valid colorings of a random graph Gn, p on n vertices with edge probability p in an online fashion. For a large family of graphs F including cliques and cycles of arbitrary size, the proposed algorithm is optimal in the following sense: for any integer r ≥ 1, there is a constant β = β(F, r) such that the algorithm a.a.s. (asymptotically almost surely) computes a valid r-coloring of Gn, p w.r.t. F online if p ≪ n-β, and any online algorithm will a.a.s. fail to do so if p ≫ n-β. That is, we observe a threshold phenomenon determined by the function n-β.