Detecting false matches in string matching algorithms

S. Muthukrishnan

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    Abstract

    Consider a text string of length n, a pattern string of length m, and a match vector of length n which declares each location in the text to be either a mismatch (the pattern does not occur beginning at that location in the text) or a potential match (the pattern may occur beginning at that location in the text). Some of the potential matches could be false, i.e., the pattern may not occur beginning at some location in the text declared to be a potential match. We investigate the complexity of two problems in this context, namely, checking if there is any false match, and identifying all the false matches in the match vector. We present an algorithm on the CRCW PRAM that checks if there exists any false match in O(1) time using O(n) processors. Since string matching takes Ω(log log m) time on the CRCW PRAM, checking for false matches is provably simpler than string matching. As an important application, we use this simple algorithm to convert the Karp-Rabin Monte Carlo type string matching algorithm into a Las Vegas type algorithm without asymptotic loss in complexity. We also present an efficient algorithm for identifying all the false matches and as a consequence, show that string matching algorithms take Ω(log log m) time even given the flexibility to output a few false matches. In addition, we give a sequential algorithm for checking using three heads on a 2-way deterministic finite slate automaton (DFA) in linear time and another on a 1-way DFA with a fixed number of heads.

    Original languageEnglish (US)
    Title of host publicationCombinatorial Pattern Matching - 4th Annual Symposium, CPM 1993, Proceedings
    EditorsAlberto Apostolico, Alberto Apostolico, Maxime Crochemore , Zvi Galil, Zvi Galil, Udi Manber
    PublisherSpringer Verlag
    Pages164-178
    Number of pages15
    ISBN (Print)9783540567646
    DOIs
    StatePublished - 1993
    EventConference of the European Society for Fuzzy Logic and Technology, EUSFLAT 2017 and 16th International Workshop on Intuitionistic Fuzzy Sets and Generalized Nets, IWIFSGN 2017 - Warsaw, Poland
    Duration: Sep 11 2017Sep 15 2017

    Publication series

    NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
    Volume684 LNCS
    ISSN (Print)0302-9743
    ISSN (Electronic)1611-3349

    Conference

    ConferenceConference of the European Society for Fuzzy Logic and Technology, EUSFLAT 2017 and 16th International Workshop on Intuitionistic Fuzzy Sets and Generalized Nets, IWIFSGN 2017
    CountryPoland
    CityWarsaw
    Period9/11/179/15/17

    ASJC Scopus subject areas

    • Theoretical Computer Science
    • Computer Science(all)

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  • Cite this

    Muthukrishnan, S. (1993). Detecting false matches in string matching algorithms. In A. Apostolico, A. Apostolico, M. Crochemore , Z. Galil, Z. Galil, & U. Manber (Eds.), Combinatorial Pattern Matching - 4th Annual Symposium, CPM 1993, Proceedings (pp. 164-178). (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); Vol. 684 LNCS). Springer Verlag. https://doi.org/10.1007/bfb0029804