Two New Families of List Update Algorithms

  • Authors:
  • Frank Schulz

  • Affiliations:
  • -

  • Venue:
  • ISAAC '98 Proceedings of the 9th International Symposium on Algorithms and Computation
  • Year:
  • 1998

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Abstract

We consider the online list accessing problem and present a new family of competitive-optimal deterministic list update algorithms which is the largest class of such algorithms known to-date. This family, called SORT-BY-RANK (SBR), is parametrized with a real 0 ≤ α ≤ 1, where SBR(0) is the MOVE-TO-FRONT algorithm and SBR(1) is equivalent to the TIMESTAMP algorithm. The behaviour of SBR(α) mediates between the eager strategy of MOVE-TO-FRONT and the more conservative behaviour of TIMESTAMP. We also present a family of algorithms SORT-BY-DELAY (SBD) which is parametrized by the positive integers, where SBD(1) is MOVE-TO-FRONT and SBD(2) is equivalent to TIMESTAMP. In general, SBD(k) is k- competitive for k ≥ 2. This is the first class of algorithms that is asymptotically optimal for independent, identically distributed requests while each algorithm is constant-competitive. Empirical studies with with both generated and real-world data are also included.