Alphabet-Independent Two-Dimensional Witness Computation

  • Authors:
  • Zvi Galil;Kunsoo Park

  • Affiliations:
  • -;-

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 1996

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Abstract

We study two-dimensional periodicity, introduced by Amir and Benson. We characterize periods of a two-dimensional array, namely, the vectors such that two copies of the array, one shifted by the vector over the other, overlap without a mismatch. Using this characterization, we design an alphabet-independent linear-time algorithm for two-dimensional witness computation, i.e., an $O(m^2)$-time algorithm that finds periods of an $m\times m$ array as well as witnesses against nonperiods of the array among the vectors whose length is less than $m/4$. The constant in the $O$ notation does not depend on the alphabet size. Combined with the alphabet-independent text-processing algorithm of Amir, Benson, and Farach [SIAM J. Comput., 23 (1994), pp.~313--323], this leads to the first alphabet-independent linear-time algorithm for two-dimensional pattern matching.