Solution -「CSP 2019」Centroid
				DescriptionLink.给定一棵 $n$ 个点的树,设 $E$ 为边集,$V'_x,\ V'_y$ 分别为删去边  $(x,y)$ 后 点  $x$ 所在的树的点集和点  $y$ 所在的...            
		In mathematics you don't understand things, you just get used to them.
In mathematics you don't understand things, you just get used to them.