提出 #75859985

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ソースコード 拡げる

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define pb push_back
#define endl '\n'

class Solution {

public:

    static const ll MOD = 998244353;

    vector<ll> fact, invFact;

    inline ll mul(ll a, ll b) {
        return (a * b) % MOD;
    }

    ll power(ll a, ll b) {

        ll ans = 1;

        while (b) {

            if (b & 1) {
                ans = mul(ans, a);
            }

            a = mul(a, a);

            b >>= 1;
        }

        return ans;
    }

    void build(ll n) {

        fact.resize(n + 1);
        invFact.resize(n + 1);

        fact[0] = 1;

        for (ll i = 1; i <= n; i++) {
            fact[i] = mul(fact[i - 1], i);
        }

        invFact[n] = power(fact[n], MOD - 2);

        for (ll i = n - 1; i >= 0; i--) {
            invFact[i] = mul(invFact[i + 1], i + 1);
        }
    }

    inline ll nCr(ll n, ll r) {

        if (r < 0 || r > n) {
            return 0;
        }

        return mul(fact[n], mul(invFact[r], invFact[n - r]));
    }

    ll solve(ll x1, ll x2, ll x3) {

        // 2 ke around gaps
        ll gaps = x2 + 1;

        ll ans = 0;

        for (ll k = 1; k <= min(x1, gaps); k++) {

            // k gaps choose for 1
            ll a = nCr(gaps, k);

            // 1s distribute
            ll b = nCr(x1 - 1, k - 1);

            ll rem = gaps - k;

            // baaki gaps me 3
            ll c = nCr(x3 + rem - 1, rem - 1);

            ll total = mul(a, mul(b, c));

            ans += total;
            ans %= MOD;
        }

        return ans;
    }
};

int main() {

    ll x1, x2, x3;
    cin >> x1 >> x2 >> x3;

    Solution obj;

    obj.build(x1 + x2 + x3 + 5);

    cout << obj.solve(x1, x2, x3) << endl;

    return 0;
}

提出情報

ジャッジ結果