Abstract
We describe a method for decomposing planar sets of segments and points. Using this method we obtain new efficientdeterministic algorithms for counting pairs of intersecting segments, and for answering off-line triangle range queries. In particular we obtain the following results:
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(1)
Givenn segments in the plane, the number of pairs of intersecting segments is counted in timeO(n 1+ɛ+K 1/3 n 2/3+ɛ), whereK is the number of intersection points among the segments, and ɛ>0 is an arbitrarily small constant.
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(2)
Givenn segments in the plane which are colored with two colors, the number of pairs ofbichromatic intersecting segments is counted in timeO(n 1+ɛ+K m 1/3 n 2/3+ɛ), whereK m is the number ofmonochromatic intersection points, and ɛ>0 is an arbitrarily small constant.
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(3)
Givenn weighted points andn triangles on a plane, the sum of weights of points in each triangle is computed in timeO(n 1+ε+ϰ1/3 n 2/3+ε), where ϰ is the number of vertices in the arrangement of the triangles, and ɛ>0 is an arbitrarily small constant.
The above bounds depend sublinearly on the number of intersections among input segmentsK (resp.K m , ϰ), which is desirable sinceK (resp.K m , ϰ) can range from zero toO(n 2). All of the above algorithms use optimal Θ(n) storage. The constants of proportionality in the big-Oh notation increase as ɛ decreases. These results are based on properties of the sparse nets introduced by Chazelle [Cha3].
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Pellegrini, M. On counting pairs of intersecting segments and off-line triangle range searching. Algorithmica 17, 380–398 (1997). https://doi.org/10.1007/BF02523679
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DOI: https://doi.org/10.1007/BF02523679