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

Boris Aronov, Mark de Berg, Jean Cardinal, Esther Ezra, John Iacono, Micha Sharir

    Research output: Contribution to journalArticlepeer-review


    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.

    Original languageEnglish (US)
    Article number101945
    JournalComputational Geometry: Theory and Applications
    StatePublished - Feb 2023


    • 3SUM-hard problems
    • Algebraic decision-tree model
    • Order type
    • Point location
    • Polynomial partitions

    ASJC Scopus subject areas

    • Computer Science Applications
    • Geometry and Topology
    • Control and Optimization
    • Computational Theory and Mathematics
    • Computational Mathematics


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