Online and offline access to short lists

  • Authors:
  • Torben Hagerup

  • Affiliations:
  • Institut für Informatik, Universität Augsburg, Augsburg, Germany

  • Venue:
  • MFCS'07 Proceedings of the 32nd international conference on Mathematical Foundations of Computer Science
  • Year:
  • 2007

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Abstract

We consider the list-update problem introduced by Sleator and Tarjan, specializing it to the case of accesses only and focusing on short lists. We describe a new optimal offline algorithm, faster than the best previous algorithm when the number of accesses is sufficiently large relative to the number l of items. We also give a simple optimal offline algorithm for l = 3. Taking cl to denote the best competitive ratio of a randomized online algorithm for the list-access problem with l items, we demonstrate that c3 = 6/5 and give new upper and lower bounds on c4. Finally we prove a strengthened lower bound for general l.