The list update problem and the retrieval of sets

  • Fabrizio d'Amore
  • Vincenzo Liberatore
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 621)


We consider the list update problem under a sequence of requests of sets of items, and for this problem we investigate the competitiveness features of two algorithms. We prove that algorithm Move-Set-to-Front (MSF) is (1+βs)-competitive, where β is the size of the largest requested set, and that a lower bound is roughly 2. We provide an upper bound to the MSF competitive ratio by relating it to the size n of the list, obtaining that the algorithm is (1+n/4)-competitive in general, and O(√n)-competitive if we add a not too restrictive constraint to the sizes of the requested sets.

We are in touch with two more problems. The first one generalizes the list update problem under a sequence of requests of sets by considering weighted lists, where a weight representing a visiting cost is associated with each item. For this case we give a competitiveness result as well.

The second one is a variant, where the list is searched to retrieve whichever element of the currently requested set (the first that can be found in the list). For this problem we provide negative results.


Cost Model Competitive Ratio Online Algorithm Competitive Algorithm Free Exchange 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 1992

Authors and Affiliations

  • Fabrizio d'Amore
    • 1
  • Vincenzo Liberatore
    • 1
  1. 1.Dipartimento di Informatica e SistemisticaUniversità di Roma “La Sapienza”RomaItaly

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