Deterministic splitter finding in a stream with constant storage and guarantees

  • Authors:
  • Tobias Lenz

  • Affiliations:
  • Freie Universität Berlin, Berlin, Germany

  • Venue:
  • ISAAC'06 Proceedings of the 17th international conference on Algorithms and Computation
  • Year:
  • 2006

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Abstract

In this paper the well-known problem of finding the median of an ordered set is studied under a very restrictive streaming model with sequential read-only access to the data. Only a constant number of reference objects from the stream can be stored for comparison with subsequent stream elements. A first non-trivial bound of $\Omega(\sqrt{n})$ distance to the extrema of the set is presented for a single pass over streams which do not reveal their total size n. For cases with known size, an algorithm is given which guarantees a distance of Ω(n1−ε) to the extrema, which is an ε-approximation for the proven best bound possible.