Clique clustering yields a PTAS for max-coloring interval graphs

  • Authors:
  • Tim Nonner

  • Affiliations:
  • IBM Research, Zurich

  • Venue:
  • ICALP'11 Proceedings of the 38th international colloquim conference on Automata, languages and programming - Volume Part I
  • Year:
  • 2011

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Abstract

We are given an interval graph G = (V,E) where each interval I ∈ V has a weight wI ∈ R+. The goal is to color the intervals V with an arbitrary number of color classes C1,C2,..., Ck such that Σi=1k maxI∈Ci wI is minimized. This problem, called max-coloring interval graphs, contains the classical problem of coloring interval graphs as a special case for uniform weights, and it arises in many practical scenarios such as memory management. Pemmaraju, Raman, and Varadarajan showed that max-coloring interval graphs is NP-hard (SODA'04) and presented a 2-approximation algorithm. Closing a gap which has been open for years, we settle the approximation complexity of this problem by giving a polynomial-time approximation scheme (PTAS), that is, we show that there is an (1+ε)-approximation algorithm for any ε 0. Besides using standard preprocessing techniques such as geometric rounding and shifting, our main building block is a general technique for trading the overlap structure of an interval graph for accuracy, which we call clique clustering.