The k-distinct language: Parameterized automata constructions

Ran Ben-Basat, Ariel Gabizon, Meirav Zehavi

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


In this paper, we pioneer a study of parameterized automata constructions for languages related to the design of parameterized algorithms. We focus on the k-Distinct language Lk(σ)⊆σk, defined as the set of words of length k over an alphabet σ whose symbols are all distinct. This language is implicitly related to several breakthrough techniques developed during the last two decades, to design parameterized algorithms for fundamental problems such as k-Path and r-Dimensional k-Matching. Building upon the color coding, divide-and-color and narrow sieves techniques, we obtain the following automata constructions for Lk(σ). We develop non-deterministic automata (NFAs) of sizes 4k+o(k)·nO(1) and (2e)k+o(k)·nO(1), where the latter satisfies a 'bounded ambiguity' property relevant to approximate counting, as well as a non-deterministic xor automaton (NXA) of size 2k·nO(1), where n=|σ|. We show that our constructions can be used to develop both deterministic and randomized algorithms for k-Path, r-Dimensional k-Matching and Module Motif in a natural manner, considering also their approximate counting variants. Our framework is modular and consists of two parts: designing an automaton for k-Distinct, and designing a problem specific automaton, as well as an algorithm for deciding whether the intersection automaton's language is empty, or for counting the number of accepting paths in it.

Original languageEnglish
Pages (from-to)1-15
Number of pages15
JournalTheoretical Computer Science
StatePublished - 4 Apr 2016
Externally publishedYes


  • Automata theory
  • K-Path
  • Parameterized complexity
  • R-Dimensional k-matching

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science (all)


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