Tight Bounds for Monotone Minimal Perfect Hashing

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Scopus citations


The monotone minimal perfect hash function (MMPHF) problem is the following indexing problem. Given a set S = {s1, ..., sn} of n distinct keys from a universe U of size u, create a data structure D that answers the following query: RANK(q) = (equation presented){rank of q in S arbitrary answer q ∈ Sotherwise. Solutions to the MMPHF problem are in widespread use in both theory and practice. The best upper bound known for the problem encodes D in O(n log log log u) bits and performs queries in O(log u) time. It has been an open problem to either improve the space upper bound or to show that this somewhat odd looking bound is tight. In this paper, we show the latter: any data structure (deterministic or randomized) for monotone minimal perfect hashing of any collection of n elements from a universe of size u requires Ω(n · log log log u) expected bits to answer every query correctly. We achieve our lower bound by defining a graph G where the nodes are the possible (un) inputs and where two nodes are adjacent if they cannot share the same D. The size of D is then lower bounded by the log of the chromatic number of G.

Original languageEnglish (US)
Title of host publication34th Annual ACM-SIAM Symposium on Discrete Algorithms, SODA 2023
PublisherAssociation for Computing Machinery
Number of pages21
ISBN (Electronic)9781611977554
StatePublished - 2023
Event34th Annual ACM-SIAM Symposium on Discrete Algorithms, SODA 2023 - Florence, Italy
Duration: Jan 22 2023Jan 25 2023

Publication series

NameProceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms


Conference34th Annual ACM-SIAM Symposium on Discrete Algorithms, SODA 2023

All Science Journal Classification (ASJC) codes

  • Software
  • General Mathematics


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