XXI Open Cup named after E.V. Pankratiev. Grand Prix of Korea

C

知道这个定理：

Theorem. A graph (G) is strongly connected if and only if it can be constructed using the following procedure:

1. Start with (N) isolated vertices. Pick any vertex (v), and let (S = {v}).
2. Repeat the following until (S = V(G)):
   (a) Pick two vertices (v) and (uin S). The two vertices can be the same.
   (b) Pick zero or more distinct vertices (w_1, cdots, w_k otin S).
   (c) Connect (v ightarrow w_1 ightarrow cdots ightarrow w_k ightarrow u), and put (w_1 cdots w_k) into (S).

然后就可以 xjb 状压 dp 了，题解给的第四维可以省掉

G

dp of dp, TODO: bzoj ATGC LCS by clj?