$\def\DD{\bf δ}\def\CH{\mathop{\mathrm{ConvexHull}}}\newcommand{\LL}{\cal {L}} \newcommand{\ZZ}{\mathbb{Z}} $ Given a convex body $C$ in the plane, its discrete hull is $C^0 = \CH( C \cap \LL )$, where $\LL = \ZZ \times \ZZ$ is the integer lattice. We present an $O( |C^0| \log \DD(C) )$-time algorithm for calculating the discrete hull of $C$, where $|C^0|$ denotes the number of vertices of $C^0$, and $\DD(C)$ is the diameter of $C$. Actually, using known combinatorial bounds, the running time of the algorithm is $O(\DD(C)^{2/3} \log{\DD(C)})$. In particular, this bound applies when $C$ is a disk.
翻译:$\def\DD{\bf δ}\def\CH{\mathop{\mathrm{ConvexHull}}}\newcommand{\LL}{\cal {L}} \newcommand{\ZZ}{\mathbb{Z}} $ 给定平面上的一个凸体 $C$,其离散凸包定义为 $C^0 = \CH( C \cap \LL )$,其中 $\LL = \ZZ \times \ZZ$ 是整数格点。我们提出了一种计算 $C$ 的离散凸包的 $O( |C^0| \log \DD(C) )$ 时间算法,其中 $|C^0|$ 表示 $C^0$ 的顶点数,$\DD(C)$ 是 $C$ 的直径。实际上,利用已知的组合界,该算法的运行时间为 $O(\DD(C)^{2/3} \log{\DD(C)})$。特别地,当 $C$ 是一个圆盘时,该界也成立。