Dynamic Conflict-Free Colorings in the Plane

We study dynamic conflict-free colorings in the plane, where the goal is to maintain a conflict-free coloring (CF-coloring for short) under insertions and deletions. - First we consider CF-colorings of a set $S$ of unit squares with respect to points. Our method maintains a CF-coloring that uses $O(\log n)$ colors at any time, where $n$ is the current number of squares in $S$, at the cost of only $O(\log n)$ recolorings per insertion or deletion of a square. We generalize the method to rectangles whose sides have lengths in the range $[1,c]$, where $c$ is a fixed constant. Here the number of used colors becomes $O(\log² n)$. The method also extends to arbitrary rectangles whose coordinates come from a fixed universe of size $N$, yielding $O(\log² N \log² n)$ colors. The number of recolorings for both methods stays in $O(\log n)$. - We then present a general framework to maintain a CF-coloring under insertions for sets of objects that admit a unimax coloring with a small number of colors in the static case. As an application we show how to maintain a CF-coloring with $O(\log³ n)$ colors for disks (or other objects with linear union complexity) with respect to points at the cost of $O(\log n)$ recolorings per insertion. We extend the framework to the fully-dynamic case when the static unimax coloring admits weak deletions. As an application we show how to maintain a CF-coloring with $O(\sqrt{n} \log² n)$ colors for points with respect to rectangles, at the cost of $O(\log n)$ recolorings per insertion and $O(1)$ recolorings per deletion. These are the first results on fully-dynamic CF-colorings in the plane, and the first results for semi-dynamic CF-colorings for non-congruent objects.