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[2209.06038] A Hash Table Without Hash Functions, and How to Get the Most Out of...

 2 years ago
source link: https://arxiv.org/abs/2209.06038
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Computer Science > Data Structures and Algorithms

[Submitted on 13 Sep 2022 (v1), last revised 15 Sep 2022 (this version, v2)]

A Hash Table Without Hash Functions, and How to Get the Most Out of Your Random Bits

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This paper considers the basic question of how strong of a probabilistic guarantee can a hash table, storing n (1 + \Theta(1)) \log n-bit key/value pairs, offer? Past work on this question has been bottlenecked by limitations of the known families of hash functions: The only hash tables to achieve failure probabilities less than 1 / 2^{\polylog n} require access to fully-random hash functions -- if the same hash tables are implemented using the known explicit families of hash functions, their failure probabilities become 1 / \poly(n).
To get around these obstacles, we show how to construct a randomized data structure that has the same guarantees as a hash table, but that \emph{avoids the direct use of hash functions}. Building on this, we are able to construct a hash table using O(n) random bits that achieves failure probability 1 / n^{n^{1 - \epsilon}} for an arbitrary positive constant \epsilon.
In fact, we show that this guarantee can even be achieved by a \emph{succinct dictionary}, that is, by a dictionary that uses space within a 1 + o(1) factor of the information-theoretic optimum.
Finally we also construct a succinct hash table whose probabilistic guarantees fall on a different extreme, offering a failure probability of 1 / \poly(n) while using only \tilde{O}(\log n) random bits. This latter result matches (up to low-order terms) a guarantee previously achieved by Dietzfelbinger et al., but with increased space efficiency and with several surprising technical components.

Subjects: Data Structures and Algorithms (cs.DS)
Cite as: arXiv:2209.06038 [cs.DS]
  (or arXiv:2209.06038v2 [cs.DS] for this version)
  https://doi.org/10.48550/arXiv.2209.06038

Submission history

From: William Kuszmaul [view email]
[v1] Tue, 13 Sep 2022 14:40:35 UTC (30 KB)
[v2] Thu, 15 Sep 2022 21:04:32 UTC (30 KB)

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