On the structure of compacted subword graphs of Thue-Morse words and their applications

  • Authors:
  • Jakub Radoszewski;Wojciech Rytter

  • Affiliations:
  • Institute of Informatics, University of Warsaw, ul. Banacha 2, 02-097 Warsaw, Poland;Institute of Informatics, University of Warsaw, ul. Banacha 2, 02-097 Warsaw, Poland

  • Venue:
  • Journal of Discrete Algorithms
  • Year:
  • 2012

Quantified Score

Hi-index 0.00

Visualization

Abstract

We investigate how syntactic properties of Thue-Morse words are related to special type of automata/graphs. The directed acyclic subword graph (dawg, in short) is a useful deterministic automaton accepting all suffixes of the word. Its compacted version (resulted by compressing chains of states) is denoted by cdawg. The cdawgs of Thue-Morse words have regular and very simple structure, in particular they offer a powerful (exponential) compression of the set of all subwords in case of finite Thue-Morse words. Using the special structure of cdawgs we present several unknown properties of Thue-Morse words as well as new (graph-based) proofs of some well-known properties. In particular we show a simple algorithm that checks, for a given string w, if w is a subword of a Thue-Morse word and computes its number of occurrences in n-th Thue-Morse word in O(|w|+logn) time and O(1) space. Additionally, a slight modification of the compact dawg of the infinite Thue-Morse word yields an infinite graph with 2-counting property.