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The Computer Journal 1998 41(6):416-421; doi:10.1093/comjnl/41.6.416
© 1998 by British Computer Society
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Quasi-perfect Hashing

Z. J. Czech

Institute of Computer Science, Silesia University, 41-200 Sosnowiec, Poland Email: zjc{at}silesia.pl

The idea of quasi-perfect hashing is introduced and applied to solve the static dictionary problem. Given a universe U and a set S of n distinct keys belonging to U, we propose a quasi-perfect hash function which allows one to find a key from S, stored in the hash table of size m, m ≤ n, in O(1) time. While looking up a key at most two probes in the hash table are made. Our main motivation is to minimize the memory requirement for representing the hashing scheme, retaining a high probability of finding quasi-perfect hash functions for arbitrary sets S. If we compare the method of quasi-perfect hashing to Fredman, Komlós and Szemerédi's two-level hashing for the bounded universe U, we find that it is superior with regard to both space and speed.

Received May 4, 1998. revised October 1, 1998.


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