Streaming algorithms for recognizing nearly well-parenthesized expressions

  • Authors:
  • Andreas Krebs;Nutan Limaye;Srikanth Srinivasan

  • Affiliations:
  • University of Tübingen, Germany;Indian Institute of Technology, Bombay, India;Institute for Advanced Study

  • Venue:
  • MFCS'11 Proceedings of the 36th international conference on Mathematical foundations of computer science
  • Year:
  • 2011

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Abstract

We study the streaming complexity of the membership problem of 1-turn-Dyck2 and Dyck2 when there are a few errors in the input string. 1-turn-Dyck2 with errors: We prove that there exists a randomized one-pass algorithm that given x checks whether there exists a string x′ ∈ 1-turn-Dyck2 such that x is obtained by flipping at most k locations of x′ using: - O(k log n) space, O(k log n) randomness, and poly(k log n) time per item and with error at most 1/nΩ(1). - O(k1+ε + log n) space for every 0 ≤ ε ≤ 1, O(log n) randomness, O((logO(1) n + kO(1))) time per item, with error at most 1/8. Here, we also prove that any randomized one-pass algorithm that makes error at most k/n requires at least Ω(k log(n/k)) space to accept strings which are exactly k-away from strings in 1-turn-Dyck2 and to reject strings which are exactly k + 2-away from strings in 1-turn-Dyck2. Since 1-turn-Dyck2 and the Hamming Distance problem are closely related we also obtain new upper and lower bounds for this problem. Dyck2 with errors: We prove that there exists a randomized one-pass algorithm that given x checks whether there exists a string x′ ∈ Dyck2 such that x is obtained from x′ by changing (in some restricted manner) at most k positions using: - O(k log n + √n log n) space, O(k log n) randomness, poly(k log n) time per element and with error at most 1/nΩ(1). - O(k1+ε + √n log n) space for every 0 O(log n) randomness, O((logO(1) n + kO(1))) time per element, with error at most 1/8.