,
Adam Górkiewicz
,
Srinivasa Rao Satti
Creative Commons Attribution 4.0 International license
We consider the 2D RMQ encoding problem: given an m× n array of mn elements over a total order, encode it such that, for any query rectangle, the position of its maximum element can be reported without accessing the original array. For m ≤ n, it is known how to encode the array in 𝒪(mn min{m, log n}) bits with 𝒪(1)-time queries [Brodal et al., Algorithmica 2012], and also how to obtain an asymptotically optimal encoding consisting of 𝒪(mn log m) bits [Brodal et al., ESA 2013]. However, the latter approach does not prove any guarantee on the query time, and it appears to be inherently sequential: it requires scanning the whole encoding to answer a query. We design a different encoding that uses near-optimal space while allowing for efficient queries. More concretely, for every parameter κ ∈ [1, log log n], our encoding uses 𝒪(κ mn(log m + log log n)) bits and answers 2D RMQ queries in 𝒪(log^{1/κ} n) time.
@InProceedings{gawrychowski_et_al:LIPIcs.ESA.2026.51,
author = {Gawrychowski, Pawe{\l} and G\'{o}rkiewicz, Adam and Satti, Srinivasa Rao},
title = {{Near-Optimal and Efficient Encoding for Two-Dimensional Range Minimum Queries}},
booktitle = {34th Annual European Symposium on Algorithms (ESA 2026)},
pages = {51:1--51:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-445-1},
ISSN = {1868-8969},
year = {2026},
volume = {388},
editor = {Bille, Philip and Pettie, Seth and Storandt, Sabine},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2026.51},
URN = {urn:nbn:de:0030-drops-271874},
doi = {10.4230/LIPIcs.ESA.2026.51},
annote = {Keywords: Encoding, Range Minimum Queries, Compact structure}
}