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Hash and Displace: Efficient Evaluation of Minimal Perfect Hash Functions

By Rasmus Pagh


A new way of constructing (minimal) perfect hash functions is described. The technique is a mixture of two well-known ones, and yields simple as well as ecient hashing schemes. More specically, the overhead associated with resolving buckets in two-level hashing schemes is reduced considerably. Evaluating a hash function requires just one multiplication and a few additions apart from primitive bit operations. The number of accesses to memory is two, one of which is to a xed location. This improves the probe performance of previous minimal perfect hashing schemes, and is shown to be optimal. The hash function description (\program") for a set of size n occupies O(n) words, and can be constructed in expected O(n) time. 1 Introduction Perfect classes of hash functions are fundamental in the study of data structures. A perfect class { dened relative to a family of datasets S { has the property that for each S 2 S it contains a \perfect function" which is 1-1 on S. We let U = f0;..

Year: 1999
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