LPF Computation Revisited

  • Authors:

  • Maxime Crochemore;Lucian Ilie;Costas S. Iliopoulos;Marcin Kubica;Wojciech Rytter;Tomasz Waleń

  • Affiliations:

  • Dept. of Computer Science, King's College London, London, UK WC2R 2LS and Université Paris-Est, France;Dept. of Computer Science, University of Western Ontario, London, Canada N6A 5B7;Dept. of Computer Science, King's College London, London, UK WC2R 2LS and Digital Ecosystems & Business Intelligence Institute, Curtin University of Technology, Perth, Australia 6845;Institute of Informatics, Warsaw University, Warszawa, Poland 02-097;Institute of Informatics, Warsaw University, Warszawa, Poland 02-097 and Dept. of Math. and Informatics, Copernicus University, Torun, Poland;Institute of Informatics, Warsaw University, Warszawa, Poland 02-097

  • Venue:
  • Combinatorial Algorithms
  • Year:
  • 2009

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Abstract

We present efficient algorithms for storing past segments of a text. They are computed using two previously computed read-only arrays (SUF and LCP) composing the Suffix Array of the text. They compute the maximal length of the previous factor (subword) occurring at each position of the text in a table called LPF. This notion is central both in many conservative text compression techniques and in the most efficient algorithms for detecting motifs and repetitions occurring in a text.The main results are: a linear-time algorithm that computes explicitly the permutation that transforms the LCP table into the LPF table; a time-space optimal computation of the LPF table; and an O(nlogn) strong in-place computation of the LPF table.