其实早就知道啊,不过apiot3之后还是在皮皮橙大神的指导下认真看了看.放一个$O(n^2)$的实现#include<bits/stdc++.h>usingu32=unsigned;usingi64=longlong;usingu64=unsignedlonglong;usingidt=std::size_t;constexpru32mod=998244353;constexpru32mul(u32