Not So Many Runs in Strings

  • Authors:
  • Mathieu Giraud

  • Affiliations:
  • CNRS, LIFL, Université Lille 1, Villeneuve d'Acsq cedex, France 59 655 and INRIA Lille Nord-Europe, Villeneuve d'Ascq, France 59 650

  • Venue:
  • Language and Automata Theory and Applications
  • Year:
  • 2008

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Abstract

Since the work of Kolpakov and Kucherov in [5,6], it is known that ρ(n), the maximal number of runs in a string, is linear in the length nof the string. A lower bound of $3/(1 + \sqrt{5})n \sim 0.927n$ has been given by Franek and al. [3,4], and upper bounds have been recently provided by Rytter, Puglisi and al., and Crochemore and Ilie (1.6n) [8.7.1]. However, very few properties are known for the ρ(n)/nfunction. We show here by a simple argument that limn→ ∞ρ(n)/nexists and that this limit is never reached. Moreover, we further study the asymptotic behavior of ρp(n), the maximal number of runs with period at most p. We provide a new bound for some microruns : we show that there is no more than 0.971 nruns of period at most 9 in binary strings. Finally, this technique improves the previous best known upper bound, showing that the total number of runs in a binary string of length nis below 1.52n.