Max-coloring and online coloring with bandwidths on interval graphs

  • Authors:
  • Sriram V. Pemmaraju;Rajiv Raman;Kasturi Varadarajan

  • Affiliations:
  • University of Iowa, Iowa City, IA;Max-Planck-Institut für Informatik, Saarbrucken, Germany;University of Iowa, Iowa City, IA

  • Venue:
  • ACM Transactions on Algorithms (TALG)
  • Year:
  • 2011

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Abstract

Given a graph G = (V, E) and positive integral vertex weights w: V → N, the max-coloring problem seeks to find a proper vertex coloring of G whose color classes C1, C2, &ldots;, Ck, minimize ∑i=1k maxv ∈ Ci w(v). This problem, restricted to interval graphs, arises whenever there is a need to design dedicated memory managers that provide better performance than the general-purpose memory management of the operating system. Though this problem seems similar to the dynamic storage allocation problem, there are fundamental differences. We make a connection between max-coloring and online graph coloring and use this to devise a simple 2-approximation algorithm for max-coloring on interval graphs. We also show that a simple first-fit strategy, that is a natural choice for this problem, yields an 8-approximation algorithm. We show this result by proving that the first-fit algorithm for online coloring an interval graph G uses no more than 8 ċ χ(G) colors, significantly improving the bound of 26 ċ χ(G) by Kierstead and Qin [1995]. We also show that the max-coloring problem is NP-hard. The problem of online coloring of intervals with bandwidths is a simultaneous generalization of online interval coloring and online bin packing. The input is a set I of intervals, each interval i∈ I having an associated bandwidth b(i) ∈ (0, 1]. We seek an online algorithm that produces a coloring of the intervals such that for any color c and any real r, the sum of the bandwidths of intervals containing r and colored c is at most 1. Motivated by resource allocation problems, Adamy and Erlebach [2003] consider this problem and present an algorithm that uses at most 195 times the number of colors used by an optimal offline algorithm. Using the new analysis of first-fit coloring of interval graphs, we show that the Adamy-Erlebach algorithm is 35-competitive. Finally, we generalize the Adamy-Erlebach algorithm to a class of algorithms and show that a different instance from this class is 30-competitive.