Worst-Case Efficient Dynamic Geometric Independent Set

TL;DR

This paper introduces a new data structure for maintaining an approximate maximum independent set of geometric objects like disks and polygons in dynamic settings, achieving sublinear worst-case update times.

Contribution

It presents the first dynamic algorithms with worst-case update bounds for geometric independent sets, using a novel deamortization scheme applicable to fat objects.

Findings

Achieves sublinear worst-case update time for dynamic independent sets.

Introduces a generic deamortization scheme for geometric objects.

Proves lower bounds showing limitations for certain classes of objects.

Abstract

We consider the problem of maintaining an approximate maximum independent set of geometric objects under insertions and deletions. We present data structures that maintain a constant-factor approximate maximum independent set for broad classes of fat objects in $d$ dimensions, where $d$ is assumed to be a constant, in sublinear \textit{worst-case} update time. This gives the first results for dynamic independent set in a wide variety of geometric settings, such as disks, fat polygons, and their high-dimensional equivalents. Our result is obtained via a two-level approach. First, we develop a dynamic data structure which stores all objects and provides an approximate independent set when queried, with output-sensitive running time. We show that via standard methods such a structure can be used to obtain a dynamic algorithm with \textit{amortized} update time bounds. Then, to obtain worst-case update time algorithms, we develop a generic deamortization scheme that with each insertion/deletion keeps (i) the update time bounded and (ii) the number of changes in the independent set constant. We show that such a scheme is applicable to fat objects by showing an appropriate generalization of a separator theorem. Interestingly, we show that our deamortization scheme is also necessary in order to obtain worst-case update bounds: If for a class of objects our scheme is not applicable, then no constant-factor approximation with sublinear worst-case update time is possible. We show that such a lower bound applies even for seemingly simple classes of geometric objects including axis-aligned rectangles in the plane.