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Subquadratic algorithms for some 3Sum-hard geometric problems in the algebraic decision-tree model

par Aronov, Boris B.;de Berg, Mark;Cardinal, Jean ;Ezra, Esther;Iacono, John ;Sharir, Micha M.
Référence Computational geometry, 109, page (101945)
Publication Publié, 2023-02

Article révisé par les pairs

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Résumé :

We present subquadratic algorithms in the algebraic decision-tree model for several 3SUM-hard geometric problems, all of which can be reduced to the following question: Given two sets A, B, each consisting of n pairwise disjoint segments in the plane, and a set C of n triangles in the plane, we want to count, for each triangle Δ∈C, the number of intersection points between the segments of A and those of B that lie in Δ. We present solutions in the algebraic decision-tree model whose cost is O(n60/31+ε), for any ε>0. Our approach is based on a primal-dual range searching mechanism, which exploits the multi-level polynomial partitioning machinery recently developed by Agarwal et al. (2021) [3]. A key step in the procedure is a variant of point location in arrangements, say of lines in the plane, which is based solely on the order type of the lines, a “handicap” that turns out to be beneficial for speeding up our algorithm.