An optimal algorithm for the (≤ k)-levels, with applications to separation and transversal problems

  • Authors:
  • Hazel Everett;Jean-Marc Robert;Marc van Kreveld

  • Affiliations:
  • -;-;-

  • Venue:
  • SCG '93 Proceedings of the ninth annual symposium on Computational geometry
  • Year:
  • 1993

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Abstract

This paper gives an optimal Onlogn+nk time algorithm for constructing the levels1,…,k in an arrangement ofn lines in the plane. This algorithmis extended to compute these levels in an arrangement ofn unboundedx-monotone polygonal convex chains,of which each pair intersects at most a constant number of times.These algorithms can be used to solve the following separation andtransversal problems. For a set nblue points and an set of n redpoints, find a line that separates the two sets in such a way that thesum, m, of the number of red pointsabove the line and the number of blue points below the line isminimized. Such an optimal line can be found in Onmlogm+nlogn time. For a set ofnline segments in the plane, find aline that intersects the maximum number of the line segments. Such anoptimal line can be found in Onmlogm+nlogn time for vertical segments and in Onmlogm+nlog2nan expected time for arbitrary line segments, wherem denotes the number ofline segments not intersected by the optimal line.