,
Tore Koß
,
Florin Manea
,
Robert Mercaş
,
Timo Specht
Creative Commons Attribution 4.0 International license
In this paper, we study a series of algorithmic problems related to the subsequences occurring in the strings of a given language, under the assumption that this language is succinctly represented by a grammar generating it, or an automaton accepting it. In particular, we focus on the following problems: Given a string w and a language L, does there exist a word of L which has w as subsequence? Do all words of L have w as a subsequence? Given an integer k alongside L, does there exist a word of L which has all strings of length k, over the alphabet of L, as subsequences? Do all words of L have all strings of length k as subsequences? For the last two problems, efficient algorithms were already presented in [Adamson et al., ISAAC 2023] for the case when L is a regular language, and efficient solutions can be easily obtained for the first two problems. We extend that work as follows: we give sufficient conditions on the class of input-languages, under which these problems are decidable; we provide efficient algorithms for all these problems in the case when the input language is context-free; we show that all problems are undecidable for context-sensitive languages. Finally, we provide a series of initial results related to a class of languages that strictly includes the regular languages and is strictly included in the class of context-sensitive languages, but is incomparable to the of class context-free languages; these results deviate significantly from those reported for language-classes from the Chomsky hierarchy.
@InProceedings{fazekas_et_al:LIPIcs.ISAAC.2024.28,
author = {Fazekas, Szil\'{a}rd Zsolt and Ko{\ss}, Tore and Manea, Florin and Merca\c{s}, Robert and Specht, Timo},
title = {{Subsequence Matching and Analysis Problems for Formal Languages}},
booktitle = {35th International Symposium on Algorithms and Computation (ISAAC 2024)},
pages = {28:1--28:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-354-6},
ISSN = {1868-8969},
year = {2024},
volume = {322},
editor = {Mestre, Juli\'{a}n and Wirth, Anthony},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2024.28},
URN = {urn:nbn:de:0030-drops-221551},
doi = {10.4230/LIPIcs.ISAAC.2024.28},
annote = {Keywords: Stringology, String Combinatorics, Subsequence, Formal Languages, Context-Free Languages, Context-Sensitive Languages}
}