Abstract
We study the following geometric hypergraph coloring problem: given a planar point set and an integer k, we wish to color the points with k colors so that any axis-aligned strip containing sufficiently many points contains all colors. We show that if the strip contains at least 2k − 1 points, such a coloring can always be found. In dimension d, we show that the same holds provided the strip contains at least k(4 ln k + ln d) points. We also consider the dual problem of coloring a given set of axis-aligned strips so that any sufficiently covered point in the plane is covered by k colors. We show that in dimension d the required coverage is at most d(k − 1) + 1. This complements recent impossibility results on decomposition of strip coverings with arbitrary orientations. From the computational point of view, we show that deciding whether a three-dimensional point set can be 2-colored so that any strip containing at least three points contains both colors is NP-complete. This shows a big contrast with the planar case, for which this decision problem is easy.
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Chargé de Recherches du FRS-FNRS.
Maître de Recherches du FRS-FNRS.
Supported by the Communauté française de Belgique - ARC.
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Aloupis, G., Cardinal, J., Collette, S. et al. Colorful Strips. Graphs and Combinatorics 27, 327–339 (2011). https://doi.org/10.1007/s00373-011-1014-5
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DOI: https://doi.org/10.1007/s00373-011-1014-5