~~不要怀疑一个1.74k通过的题目~~
by dbxxx @ 2020-05-03 15:44:19
而且你咋得来的2^3啊
by dbxxx @ 2020-05-03 15:45:01
醒醒，答案是$2^{n-1}$
by Mine_King @ 2020-05-03 15:51:20
$ans=C_3^2+C_3^0$
`i取从0到n所有偶数`
by Fatalis_Lights @ 2020-05-03 16:13:22
@[davidlyd](/user/245292)
by Fatalis_Lights @ 2020-05-03 16:14:47
是呀明明是8
by Rain_cyl @ 2020-05-05 17:18:47
@[abinchen](/user/288650) i取从0到n所有**偶数**
by zxyluogu @ 2021-11-14 14:01:22