Applications of Incidence Bounds in Point Covering Problems

In the Line Cover problem a set of n points is given and the task is to cover the points using either the minimum number of lines or at most k lines. In Curve Cover, a generalization of Line Cover, the task is to cover the points using curves with d degrees of freedom. Another generalization is the Hyperplane Cover problem where points in d-dimensional space are to be covered by hyperplanes. All these problems have kernels of polynomial size, where the parameter is the minimum number of lines, curves, or hyperplanes needed. First we give a non-parameterized algorithm for both problems in O∗(2n) (where the O∗(·) notation hides polynomial factors of n) time and polynomial space, beating a previous exponentialspace result. Combining this with incidence bounds similar to the famous Szemerédi-Trotter bound, we present a Curve Cover algorithm with running time O∗ ( (Ck/ log k)(d−1)k ) , where C is some constant. Our result improves the previous best times O∗ ( (k/1.35) ) for Line Cover (where d = 2), O∗ ( k ) for general Curve Cover, as well as a few other bounds for covering points by parabolas or conics. We also present an algorithm for Hyperplane Cover in R3 with running time O∗ ( (Ck2/ log1/5k)k ) , improving on the previous time of O∗ ( (k2/1.3)k ) . 1998 ACM Subject Classification F.2.2 Nonnumerical Algorithms and Problems