Geometric streaming algorithms with a sorting primitive

  • Authors:
  • Eric Y. Chen

  • Affiliations:
  • School of Computer Science, University of Waterloo, Waterloo, ON, Canada

  • Venue:
  • ISAAC'07 Proceedings of the 18th international conference on Algorithms and computation
  • Year:
  • 2007

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Abstract

We solve several fundamental geometric problems under a new streaming model recently proposed by Ruhl et al. [2,12]. In this model, in one pass the input stream can be scanned to generate an output stream or be sorted based on a user-defined comparator; all intermediate streams must be of size O(n). We obtain the following geometric results for any fixed constant Ɛ 0: - We can construct 2D convex hulls in O(1) passes with O(nƐ) extra space. - We can construct 3D convex hulls in O(1) expected number of passes with O(nƐ) extra space. - We can construct a triangulation of a simple polygon in O(1) expected number of passes with O(nƐ) extra space, where n is the number of vertices on the polygon. - We can report all k intersections of a set of 2D line segments in O(1) passes with O(nƐ) extra space, if an intermediate stream of size O(n + k) is allowed. We also consider a weaker model, where we do not have the sorting primitive but are allowed to choose a scan direction for every scan pass. Here we can construct a 2D convex hull from an x-ordered point set in O(1) passes with O(nƐ) extra space.