毒瘤预警
by wuzhaoxin @ 2019-01-14 19:26:56
毒瘤预警
by 小粉兔 @ 2019-01-14 19:31:01
@[小粉兔](/space/show?uid=10703) orz
by NaCly_Fish @ 2019-01-14 19:31:44
f[l][r][k][x]=c[x-l+k][k]*c[r-x+k][k]
c是组合数
by 142857cs @ 2019-01-14 19:32:58
楼上神仙
by GNAQ @ 2019-01-14 19:39:13
@[142857cs](/space/show?uid=35760) orz orz感谢大佬
by NaCly_Fish @ 2019-01-14 19:42:31
g像是FFT啊
by ddwqwq @ 2019-01-14 19:43:06
用FFT转移
by ddwqwq @ 2019-01-14 19:44:06
但不是单点的
by ddwqwq @ 2019-01-14 19:45:22
f 已经有人回答了，简单推一下 g。
```latex
G_k(z)=\sum_n g_{n,k}z^n=\frac1{(1-z)^2}G_{k-1}(z)=\frac{z}{(1-z)^{2k+1}}
```
因此 $g_{n,k}=\binom{-2k-1}{n-1}(-1)^{-2k-1}=\binom{2k+n-1}{2k}$
by Elegia @ 2019-01-14 19:54:16