传送门
code
/*************************************************************************
> File Name: 1.cpp
> Author: Knowledge_llz
> Mail: 925538513@qq.com
> Blog: https://www.cnblogs.com/Knowledge-Pig/
************************************************************************/
#include<bits/stdc++.h>
#define LL long long
#define endl '\n'
using namespace std;
const int mod = 998244353, maxx = 3e5;
LL n, m, k, fac[maxx], inv[maxx], ans;
LL qpow(LL x, LL y){
LL res = 1;
while(y){
if(y & 1) res = res * x % mod;
x = x * x % mod;
y >>= 1;
}
return res;
}
void init(){
fac[0] = 1;
for(int i = 1; i <= maxx - 10; ++i) fac[i] = fac[i - 1] * i % mod;
inv[maxx - 10] = qpow(fac[maxx - 10], mod - 2);
for(int i = maxx - 11; i >= 0; --i) inv[i] = inv[i + 1] * (i + 1) % mod;
}
LL C(int n, int m){
if(n < 0 || m < 0 || n < m) return 0;
return fac[n] * inv[m] % mod * inv[n - m] % mod;
}
int main(){
ios::sync_with_stdio(false); cin.tie(0);
#ifndef ONLINE_JUDGE
freopen("input.in", "r", stdin);
freopen("output.out","w", stdout);
#endif
init();
cin >> n >> m >> k;
ans = C(n, m);
for(int i = 1, fg = -1; i <= n - m + 1; ++i){
ans = (ans + fg * C(n - m + 1, i) * C(n - i * (k + 1), n - m)) % mod;
fg *= -1;
};
LL ans1 = ans; ans = 0;
ans = C(n, m);
for(int i = 1, fg = -1; i <= n - m + 1; ++i){
ans = (ans + fg * C(n - m + 1, i) * C(n - i * k, n - m)) % mod;
fg *= -1;
}
cout << ((ans1 - ans) % mod + mod) % mod << endl;
return 0;
}