Approximability of (Simultaneous) Class Cover for Boxes

TL;DR

This paper proves APX-hardness for the Boxes Class Cover problem and its symmetric variant, providing new bounds on approximability and a polynomial-time approximation algorithm for the symmetric case.

Contribution

It offers an alternative proof of APX-hardness for the Boxes Class Cover problem, extends results to general position and half-strips, and introduces and approximates the symmetric variant.

Findings

APX-hardness established for Boxes Class Cover and symmetric variant

Explicit lower bounds on approximability provided

Polynomial-time constant-factor approximation algorithm for the symmetric variant

Abstract

Bereg et al. (2012) introduced the Boxes Class Cover problem, which has its roots in classification and clustering applications: Given a set of n points in the plane, each colored red or blue, find the smallest cardinality set of axis-aligned boxes whose union covers the red points without covering any blue point. In this paper we give an alternative proof of APX-hardness for this problem, which also yields an explicit lower bound on its approximability. Our proof also directly applies when restricted to sets of points in general position and to the case where so-called half-strips are considered instead of boxes, which is a new result. We also introduce a symmetric variant of this problem, which we call Simultaneous Boxes Class Cover and can be stated as follows: Given a set S of n points in the plane, each colored red or blue, find the smallest cardinality set of axis-aligned boxes which together cover S such that all boxes cover only points of the same color and no box covering a red point intersects a box covering a blue point. We show that this problem is also APX-hard and give a polynomial-time constant-factor approximation algorithm.