比如 $C_4 H_{10}$ 有两种，分别是正丁烷和异丁烷。
by SMT0x400 @ 2024-03-19 15:25:14
@[SMT0x400](/user/121995) [P6598 烷烃计数 ](https://www.luogu.com.cn/problem/P6598)
by User_Unauthorized @ 2024-03-19 15:33:41
@[User_Unauthorized](/user/746760) 谢谢，头大了
by SMT0x400 @ 2024-03-19 16:16:13