Spiral Galaxies is a pencil-and-paper puzzle played on a grid of unit squares: given a set of points called centers, the goal is to partition the grid into polyominoes such that each polyomino contains exactly one center and is $180^\circ$ rotationally symmetric about its center. We show that this puzzle is NP-complete even if the polyominoes are restricted to be (a) rectangles of arbitrary size or (b) 1$\times$1, 1$\times$3, and 3$\times$1 rectangles. The proof for the latter variant also implies NP-completeness of finding a non-crossing matching in modified grid graphs where edges connect vertices of distance $2$. Moreover, we prove NP-completeness of the design problem of minimizing the number of centers such that there exist a set of Spiral Galaxies that exactly cover a given shape.
翻译:螺旋星系是一个在单位方格网格上播放的铅笔和纸的拼图 : 如果有一组点称为中心, 目标是将网格分割成多聚人种, 这样每个聚聚虫体就包含一个完全的中枢, 其中心旋转对称为 180 ⁇ circ$ 。 我们显示这个拼图是全 NP 的, 即使多聚人种被限制为 (a) 任意大小的矩形或 (b) 1 $\ times$ 1, 1 $\ times 3 和 3$\ times $ 1 矩形。 后一种变种的证明也意味着在修改的网格图中找到非交叉匹配的 NP, 其中边缘连接距离的脊椎为$2 。 此外, 我们证明在最小化中心数量的设计问题上NP 的完整性, 即最小化中心的数量, 这样有一套正覆盖给定形状的螺旋键。