为啥要减一？？？
by fashoint @ 2019-05-04 18:11:18
你要是 f[0] = 0，那就不用减 1 了
by 小粉兔 @ 2019-05-04 18:41:08
[@小粉兔](https://www.luogu.org/space/show?uid=10703)
谢谢，明白了
by fashoint @ 2019-05-06 16:13:57