Kortit II

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

int mod = 1e9 + 7;

unordered_map<int, int> muistiBinomi;
long long binomikerroin(int n, int k)
{
    if (k > (n >> 1))
        return binomikerroin(n, n - k);

    if (k == 0)
        return 1LL;

    int a = n * 1002 + k;
    auto v = muistiBinomi.find(a);
    if (v != muistiBinomi.end())
    {
        return (long long)(v->second);
    }

    int tulos = (binomikerroin(n - 1, k - 1) + binomikerroin(n - 1, k)) % mod;
    muistiBinomi[a] = tulos;
    return (long long)tulos;
}

unordered_map<int, int> muisti;

long long laske(int n, int r)
{
    if (n == 0)
        return 0;
    if (n == r + 1 || r == 1)
        return 1;

    int a = n * 1002 + r;
    auto v = muisti.find(a);
    if (v != muisti.end())
    {
        return (long long)(v->second);
    }

    // r * laske(n - 1, r) + (n - r) * laske(n - 1, r - 1) + (n - 1) * laske(n - 2, r - 1)
    int tulos = ((r * laske(n - 1, r)) % mod + ((n - r) * laske(n - 1, r - 1)) % mod + ((n - 1) * laske(n - 2, r - 1)) % mod) % mod;
    muisti[a] = tulos;
    return (long long)tulos;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int t, n, a, b;
    cin >> t;

    int kertomat[2001];
    kertomat[1] = 1;

    for (long long i = 2; i <= 2000; i++)
    {
        kertomat[i] = (kertomat[i - 1] * i) % mod;
    }

    /*for (int y = 0; y < 10; y++)
    {
        for (int x = 0; x <= y; x++)
        {
            cout << binomikerroin(y, x) << " ";
        }
        cout << "\n";
    }*/

    for (int i = 0; i < t; i++)
    {
        cin >> n >> a >> b;
        int voittoja = a + b;

        if (voittoja < 0 || voittoja > n || ((a == 0) ^ (b == 0)))
        {
            cout << "0\n";
            continue;
        }

        if (a == 0 && b == 0)
        {
            cout << kertomat[n] << "\n";
            continue;
        }

        int tasapeleja = binomikerroin(n, n - voittoja);

        long long ereja = laske(voittoja, min(a, b));

        cout << (((ereja * tasapeleja) % mod) * kertomat[n]) % mod << "\n";
    }
}

Test 1

Group: 1, 2, 3, 4, 5

Verdict: ACCEPTED

Test 2

Group: 2, 3, 4, 5

Verdict: ACCEPTED

Test 3

Group: 3, 4, 5

Verdict: ACCEPTED

Test 4

Group: 4, 5

Verdict: ACCEPTED

Test 5

Group: 5

Verdict: ACCEPTED

Test 6

Group: 5

Verdict: ACCEPTED