Towards optimal multiple selection

  • Authors:
  • Kanela Kaligosi;Kurt Mehlhorn;J. Ian Munro;Peter Sanders

  • Affiliations:
  • Max Planck Institut für Informatik, Saarbrücken, Germany;Max Planck Institut für Informatik, Saarbrücken, Germany;University of Waterloo, Ontario, Canada;Universität Karlsruhe, Germany

  • Venue:
  • ICALP'05 Proceedings of the 32nd international conference on Automata, Languages and Programming
  • Year:
  • 2005

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Abstract

The multiple selection problem asks for the elements of rank r1, r2, ..., rk from a linearly ordered set of n elements. Let B denote the information theoretic lower bound on the number of element comparisons needed for multiple selection. We first show that a variant of multiple quickselect — a well known, simple, and practical generalization of quicksort — solves this problem with $B+\mathcal{O}(n)$ expected comparisons. We then develop a deterministic divide-and-conquer algorithm that solves the problem in $\mathcal{O}(B)$ time and $B+o(B)+\mathcal{O}(n)$ element comparisons.