A probabilistic algorithm for the post office problem

  • Authors:
  • K Clarkson

  • Affiliations:
  • AT&T Bell Laboratories, Murray Hill, New Jersey

  • Venue:
  • STOC '85 Proceedings of the seventeenth annual ACM symposium on Theory of computing
  • Year:
  • 1985

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Abstract

The post office problem is the following: points in d-dimensional space, so that given an arbitrary point p, the closest points in S to p can be found quickly.We consider the case of this problem where the Euclidean norm is the measure of distance. The previous best algorithm for this problem for d2 requires &Ogr;(n2d+1) preprocessing time to build a data structure allowing an &Ogr;(log n query time. We will show that a data structure can be built in expected &Ogr;(n(d-1)(1+k)) time, for any fixed k;&Ogr;, so that closest-point queries can be answered in &Ogr;(log n) worstcase time. (The constant factors depend on d and k.) The algorithm employs random sampling, so the expected time holds for any set of points. A variant of this algorithm (for the variant problem where only one closest point of S to the query point is desired) requires &Ogr;(n⌈d/2⌉) &ogr;(n⌈d/2⌉) preprocessing time for &ogr;(nt) worst-case query time, for any fixed &egr;0. These results approach the &OHgr;(n⌈d/2⌉) preprocessing time required for any algorithm constructing the Voronoi diagram of the input points. Implementation of these algorithms requires not too much more than a random sampling procedure and a procedure for constructing the Voronoi diagram of that random sample.