提出 #75859688

---

ソースコード 拡げる

#include <iostream>
#include <vector>
using namespace std;
const int MOD = 998244353;
const int MAX = 3000005;
long long modpow(long long a, long long e) {
    long long res = 1;
    while (e) {
        if (e & 1) res = res * a % MOD;
        a = a * a % MOD;
        e >>= 1;
    }
    return res;
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int X1, X2, X3;
    cin >> X1 >> X2 >> X3;
    int M = X2 + 1;
    int Nmax = X1 + X2 + X3 + 5;
    vector<long long> fact(Nmax + 1), invfact(Nmax + 1);
    fact[0] = 1;
    for (int i = 1; i <= Nmax; ++i)
        fact[i] = fact[i-1] * i % MOD;
    invfact[Nmax] = modpow(fact[Nmax], MOD-2);
    for (int i = Nmax-1; i >= 0; --i)
        invfact[i] = invfact[i+1] * (i+1) % MOD;
    auto C = [&](int n, int k) -> long long {
        if (k < 0 || k > n) return 0;
        return fact[n] * invfact[k] % MOD * invfact[n-k] % MOD;
    };
    long long ans = 0;
    int lim = min(X1, M);
    for (int i = 1; i <= lim; ++i) {
        int rem = M - i;
        if (rem == 0) continue;
        long long ways = C(M, i) * C(X1 - 1, i - 1) % MOD;
        ways = ways * C(X3 + rem - 1, rem - 1) % MOD;
        ans = (ans + ways) % MOD;
    }
    cout << ans;
    return 0;
}

提出情報

ジャッジ結果