$\cdots \times \dfrac{2}{\frac{2}{4}}$ 即 $\Theta(n)$。 by Coros_Trusds @ 2021-08-04 11:37:10
断掉边(2->1)和(1->3)连上(2->3)和(4->1) by yqw2486 @ 2021-12-27 11:16:06