Efficient Minimal Perfect Hashing in Nearly Minimal Space

  • Authors:
  • Torben Hagerup;Torsten Tholey

  • Affiliations:
  • -;-

  • Venue:
  • STACS '01 Proceedings of the 18th Annual Symposium on Theoretical Aspects of Computer Science
  • Year:
  • 2001

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Abstract

We consider the following problem: Given a subset S of size n of a universe {0,..., u-1}, construct a minimal perfect hash function for S, i.e., a bijection h from S to {0,..., n - 1}. The parameters of interest are the space needed to store h, its evaluation time, and the time required to compute h from S. The number of bits needed for the representation of h, ignoring the other parameters, has been thoroughly studied and is known to be n log e + loglog u ± O(log n), where "log" denotes the binary logarithm. A construction by Schmidt and Siegel uses O(n + loglogu) bits and offers constant evaluation time, but the time to find h is not discussed. We present a simple randomized scheme that uses n log e+log log u+o(n+log log u) bits and has constant evaluation time and O(n + log log u) expected construction time.