Anchored Rectangle and Square Packings

Abstract: For points $p_1,\ldots , p_n$ in the unit square $[0,1]^2$, an \emph{anchored rectangle packing} consists of interior-disjoint axis-aligned empty rectangles $r_1,\ldots , r_n\subseteq [0,1]^2$ such that point $p_i$ is a corner of the rectangle $r_i$ (that is, $r_i$ is \emph{anchored} at $p_i$) for $i=1,\ldots, n$. We show that for every set of $n$ points in $[0,1]^2$, there is an anchored rectangle packing of area at least $7/12-O(1/n)$, and for every $n\in \mathbf{N}$, there are point sets for which the area of every anchored rectangle packing is at most $2/3$. The maximum area of an anchored \emph{square} packing is always at least $5/32$ and sometimes at most $7/27$. The above constructive lower bounds immediately yield constant-factor approximations, of $7/12 -\varepsilon$ for rectangles and $5/32$ for squares, for computing anchored packings of maximum area in $O(n\log n)$ time. We prove that a simple greedy strategy achieves a $9/47$-approximation for anchored square packings, and $1/3$ for lower-left anchored square packings. Reductions to maximum weight independent set (MWIS) yield a QPTAS and a PTAS for anchored rectangle and square packings in $n^{O(1/\varepsilon)}$ and $\exp({\rm poly}(\log (n/\varepsilon)))$ time, respectively.