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A generalised degenerate string (GD string) S^ is a sequence of n sets of strings of total size N, where the ith set contains strings of the same length k_i but this length can vary between different sets. We denote the sum of these lengths k_0, k_1,...,k_{n-1} by W. This type of uncertain sequence can represent, for example, a gapless multiple sequence alignment of width W in a compact form. Our first result in this paper is an O(N+M)-time algorithm for deciding whether the intersection of two GD strings of total sizes N and M, respectively, over an integer alphabet, is non-empty. This result is based on a combinatorial result of independent interest: although the intersection of two GD strings can be exponential in the total size of the two strings, it can be represented in only linear space. A similar result can be obtained by employing an automata-based approach but its cost is alphabet-dependent. We then apply our string comparison algorithm to compute palindromes in GD strings. We present an O(min{W,n^2}N)-time algorithm for computing all palindromes in S^. Furthermore, we show a similar conditional lower bound for computing maximal palindromes in S^. Finally, proof-of-concept experimental results are presented using real protein datasets.
@InProceedings{alzamel_et_al:LIPIcs.WABI.2018.21,
author = {Alzamel, Mai and Ayad, Lorraine A. K. and Bernardini, Giulia and Grossi, Roberto and Iliopoulos, Costas S. and Pisanti, Nadia and Pissis, Solon P. and Rosone, Giovanna},
title = {{Degenerate String Comparison and Applications}},
booktitle = {18th International Workshop on Algorithms in Bioinformatics (WABI 2018)},
pages = {21:1--21:14},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-082-8},
ISSN = {1868-8969},
year = {2018},
volume = {113},
editor = {Parida, Laxmi and Ukkonen, Esko},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WABI.2018.21},
URN = {urn:nbn:de:0030-drops-93236},
doi = {10.4230/LIPIcs.WABI.2018.21},
annote = {Keywords: degenerate strings, generalised degenerate strings, elastic-degenerate strings, string comparison, palindromes}
}