AI中文摘要
我们研究了一种 $k$ 连珠游戏的变体,其中玩家交替占据位置,直到所有被占据的位置中出现 $k$ 连珠。这导致了对配置的近 $k$ 连珠避免约束,以及确定此类配置的极值密度的相关问题。我们在两种棋盘上研究这个问题:网格 $\mathbb{Z}^2$ 和超立方体 $[k]^d$。对于网格 $\mathbb{Z}^2$,我们建立了最大密度 $D(k,\mathbb{Z}^2)$ 的几乎紧界,证明当 $3\ mid k$ 时 $D(k,\mathbb{Z}^2)=1-\ rac{2}{k}$,并精确确定了 $D(3,\mathbb{Z}^2)$ 和 $d(3,\mathbb{Z}^2)$。我们还给出了最小密度 $d(k,\mathbb{Z}^2)$ 的界,其差距为 $(8+o(1))k^{-1}$。对于超立方体 $[k]^d$,我们推导出 $D(k,[k]^d)$ 的渐近界,阶为 $k^{-2}$,并得到了 $d(k,[k]^d)$ 的精确值。我们的结果与经典的 no-$(k+1)$-in-line 问题形成对比,后者施加了不同的约束,且其平凡上界被猜想可达。
英文摘要
We study a variant of the $k$-in-a-row game in which players alternatively claim positions until a $k$-in-a-row is created among all claimed positions. This leads to the constraint near $k$-in-a-row avoiding on configurations and the associated problem of determining their extremal densities of such configurations.
We investigate this problem on two types of boards: the grid $\mathbb{Z}^2$ and hypercubes $[k]^d$. For the grid $\mathbb{Z}^2$, we establish nearly tight bounds on the maximum density $D(k,\mathbb{Z}^2)$, showing that $D(k,\mathbb{Z}^2)=1-\frac{2}{k}$ whenever $3\nmid k$, and determine both $D(3,\mathbb{Z}^2)$ and $d(3,\mathbb{Z}^2)$ exactly. We also bound the minimum density $d(k,\mathbb{Z}^2)$ up to a gap of $(8+o(1))k^{-1}$. For hypercubes $[k]^d$, we derive asymptotic bounds on $D(k,[k]^d)$ up to order $k^{-2}$ and obtain the exact value of $d(k,[k]^d)$. Our results contrast with the classical no-$(k+1)$-in-line problem, a similar problem imposing different constraint, where the trivial upper bound is conjectured to be attainable.