这个题解错了网上还没有题解 囧

fi = (i%2)? 1 : -1

Fn = (n+m−1m−1) - ∑ni=0 ∑m−1j=1 (n−i∗(j+1)+m−2 m−2) * (m−1 j)*fj

Fn *= m

#include
     
      using namespace std;typedef long long ll;const int MAXN = 1e5+5;const int MOD = 998244353;ll C[1005][1005];int main(){    int n,m;    C[0][0] = 1;    for(int i = 1; i <= 1000; ++i) {        C[i][0] = C[i][i] = 1;        for(int j = 1; j < i; ++j) {            C[i][j] = (C[i-1][j-1]+C[i-1][j]) %MOD;        }    }    while(~scanf("%d %d",&n,&m)) {        ll ans = C[n+m-1][m-1];        for(int i = 0; i <= n; ++i) {            int fl = -1;            for(int j = 1; j <= m-1; ++j) {                if(n-i*(j+1) < 0) continue;                int tt = n-i*(j+1);                ans = (ans + fl*C[tt+m-2][m-2]*C[m-1][j]%MOD + MOD) %MOD;                fl *= -1;                               }        }        printf("%lld\n",ans*m%MOD);    }    return 0;}