A covering path for a planar point set is a path drawn in the plane with straight-line edges such that every point lies at a vertex or on an edge of the path. A covering tree is defined analogously. Let $\pi(n)$ be the minimum number such that every set of $n$ points in the plane can be covered by a noncrossing path with at most $\pi(n)$ edges. Let $\tau(n)$ be the analogous number for noncrossing covering trees. Dumitrescu, Gerbner, Keszegh, and T\'oth (Discrete & Computational Geometry, 2014) established the following inequalities: \[\frac{5n}{9} - O(1) < \pi(n) < \left(1-\frac{1}{601080391}\right)n, \quad\text{and} \quad\frac{9n}{17} - O(1) < \tau(n)\leqslant \left\lfloor\frac{5n}{6}\right\rfloor.\] We report the following improved upper bounds: \[\pi(n)\leqslant \left(1-\frac{1}{22}\right)n, \quad\text{and}\quad \tau(n)\leqslant \left\lceil\frac{4n}{5}\right\rceil.\] In the same context we study rainbow polygons. For a set of colored points in the plane, a perfect rainbow polygon is a simple polygon that contains exactly one point of each color in its interior or on its boundary. Let $\rho(k)$ be the minimum number such that every $k$-colored point set in the plane admits a perfect rainbow polygon of size $\rho(k)$. Flores-Pe\~naloza, Kano, Mart\'inez-Sandoval, Orden, Tejel, T\'oth, Urrutia, and Vogtenhuber (Discrete Mathematics, 2021) proved that $20k/19 - O(1) <\rho(k) < 10k/7 + O(1).$ We report the improved upper bound $\rho(k)< 7k/5 + O(1)$. To obtain the improved bounds we present simple $O(n\log n)$-time algorithms that achieve paths, trees, and polygons with our desired number of edges.

翻译：对于平面点集而言，一条覆盖路径是指用直线段边在平面上绘制的一条路径，使得每个点要么位于路径的顶点上，要么位于路径的边上。覆盖树的定义类似。设π(n)为最小整数，使得平面内任意n个点集均可被一条边数不超过π(n)的无交叉路径所覆盖。设τ(n)为无交叉覆盖树的相应数值。Dumitrescu、Gerbner、Keszegh与Tóth（《离散与计算几何》，2014年）建立了以下不等式：\[\frac{5n}{9} - O(1) < \pi(n) < \left(1-\frac{1}{601080391}\right)n, \quad\text{及} \quad\frac{9n}{17} - O(1) < \tau(n)\leqslant \left\lfloor\frac{5n}{6}\right\rfloor.\] 本文报告以下改进的上界：\[\pi(n)\leqslant \left(1-\frac{1}{22}\right)n, \quad\text{及}\quad \tau(n)\leqslant \left\lceil\frac{4n}{5}\right\rceil.\] 在同一背景下，我们研究了彩虹多边形。对于平面内一组彩色点，一个完美彩虹多边形是指一个简单多边形，其内部或边界上恰好包含每种颜色的一个点。设ρ(k)为最小整数，使得平面内任意k色点集均存在一个大小为ρ(k)的完美彩虹多边形。Flores-Peñaloza、Kano、Martínez-Sandoval、Orden、Tejel、Tóth、Urrutia与Vogtenhuber（《离散数学》，2021年）证明了\(20k/19 - O(1) < \rho(k) < 10k/7 + O(1).\) 本文报告改进的上界\(\rho(k)< 7k/5 + O(1)\). 为获得这些改进的上界，我们提出了简单的\(O(n\log n)\)时间算法，以生成具有所需边数的路径、树和多边形。