An orientable sequence of order n is a cyclic binary sequence such that each length-n substring appears at most once in either direction. Maximal length orientable sequences are known only for n ≤ 7, and a trivial upper bound on their length is 2^{n-1} - 2^{⌊(n-1)/2⌋}. This paper presents the first efficient algorithm to construct orientable sequences with asymptotically optimal length; more specifically, our algorithm constructs orientable sequences via cycle-joining and a successor-rule approach requiring O(n) time per bit and O(n) space. This answers a longstanding open question from Dai, Martin, Robshaw, Wild [Cryptography and Coding III (1993)]. Our sequences are applied to find new longest-known orientable sequences for n ≤ 20.
@InProceedings{gabric_et_al:LIPIcs.CPM.2024.15, author = {Gabri\'{c}, Daniel and Sawada, Joe}, title = {{Efficient Construction of Long Orientable Sequences}}, booktitle = {35th Annual Symposium on Combinatorial Pattern Matching (CPM 2024)}, pages = {15:1--15:12}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-326-3}, ISSN = {1868-8969}, year = {2024}, volume = {296}, editor = {Inenaga, Shunsuke and Puglisi, Simon J.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CPM.2024.15}, URN = {urn:nbn:de:0030-drops-201255}, doi = {10.4230/LIPIcs.CPM.2024.15}, annote = {Keywords: orientable sequence, de Bruijn sequence, concatenation tree, cycle-joining, universal cycle} }
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