Average case selection

  • Authors:
  • Walter Cunto;J. Ian Munro

  • Affiliations:
  • -;-

  • Venue:
  • STOC '84 Proceedings of the sixteenth annual ACM symposium on Theory of computing
  • Year:
  • 1984

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Abstract

We consider problems such as selecting the k-th smallest of n numbers in as few comparisons as possible on average. n + k - 0(1) comparisons are proved to be necessary for this particular problem when k ≤ n/2. This shows a technique of Floyd and Rivest is essentially optimal. 7n/4 &equil; o(n) comparisons, on average, are shown to be necessary and sufficient to find the maximum and median of a set. An upper bound of 9n/4 + o(n) and a lower bound of 2n − o(n) are shown for the max-min-median problem.