,
Mirko Giacchini
,
Ravi Kumar
,
Erasmo Tani
Creative Commons Attribution 4.0 International license
Locality-sensitive hashing (LSH) has found widespread use as a fundamental primitive, particularly to accelerate nearest neighbor search. An LSH scheme for a similarity function S:π³ Γ π³ β [0,1] is a distribution over hash functions on π³ with the property that the probability of collision of any two elements x,y β π³ is exactly equal to S(x,y). However, not all similarity functions admit exact LSH schemes. The notion of LSH distortion measures how multiplicatively close a similarity function is to having an LSH scheme.
In this work, we study the LSH distortion of the Ulam and Cayley similarities, which are popular similarity measures on permutations of n elements. We show that the Ulam similarity admits a sublinear LSH distortion of O(n/β{log n}); we also prove a lower bound of Ξ©(n^{0.12}) on the best LSH distortion achievable. On the other hand, we show that the LSH distortion of the Cayley similarity is Ξ(n).
@InProceedings{chierichetti_et_al:LIPIcs.APPROX/RANDOM.2026.59,
author = {Chierichetti, Flavio and Giacchini, Mirko and Kumar, Ravi and Tani, Erasmo},
title = {{On the LSH Distortion of Ulam and Cayley Similarities}},
booktitle = {Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2026)},
pages = {59:1--59:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-449-9},
ISSN = {1868-8969},
year = {2026},
volume = {392},
editor = {Singh, Mohit and Gur, Tom},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.APPROX/RANDOM.2026.59},
URN = {urn:nbn:de:0030-drops-277765},
doi = {10.4230/LIPIcs.APPROX/RANDOM.2026.59},
annote = {Keywords: Locality-sensitive Hashing, Ulam metric, Cayley Metric, Distortion, Permutations, Representation Theory}
}