Optimal randomized comparison based algorithms for collision

  • Authors:
  • Riko Jacob

  • Affiliations:
  • Computer Science Department, Technische Universität München

  • Venue:
  • MFCS'07 Proceedings of the 32nd international conference on Mathematical Foundations of Computer Science
  • Year:
  • 2007

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Abstract

We consider the well known problem of finding two identical elements, called a collision, in a list of n numbers. Here, the (very fast) comparison based algorithms are randomized and will only report existing collisions, and do this with (small) probability p, the success probability. We find a trade-off between p and the running time t, and show that this trade-off is optimal up to a constant factor. For worst-case running time t, the optimal success probability is p = Θ(min{t/n, 1}t/(n log t)). For expected running time t, the success probability is p = Θ(t/(n log n)).