Kortit II

input/code.cpp: In function 'int main()':
input/code.cpp:58:42: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   58 |                 if (a + b > n || mm == 0 && ma != 0) {
      |                                  ~~~~~~~~^~~~~~~~~~

#include <iostream>

typedef long long ll;

using namespace std;

const ll mod = 1000000007;

ll d[2020][2020];
ll f[2020];

void construct() {
	int n = 2000; int k = 2000;
	
	for (int i = 2; i <= n; i++) d[i][1] = 1;

	for (int i = 3; i <= n; i++) {
		for (int j = 2; j <= k; j++) {
			d[i][j] = (i - 1) * (d[i - 2][j - 1]) + (i - j) * d[i - 1][j - 1] + j * (d[i - 1][j]);
			d[i][j] %= mod;
		}
	}

	ll s = 1;
	for (ll i = 1; i <= k; i++) {
		s *= i;
		s %= mod;
		f[i] = s;
	}
}

ll pot(ll x, ll y, ll m) {
	if (y == 0) return 1 % m;
	ll u = pot(x, y / 2, m);
	u = (u * u) % m;
	if (y % 2 == 1) u = (u * x) % m;
	return u;
}

ll binom(ll a, ll b) {
	return f[a] * pot(f[b] * f[a - b] % mod, mod - 2, mod) % mod;
}

int main() {

	construct();

	int t;
	cin >> t;
	while (t) {
		t--;
		ll n, a, b;
		cin >> n >> a >> b;

		ll mm = (a < b) ? a : b;
		ll ma = (a > b) ? a : b;

		if (a + b > n || mm == 0 && ma != 0) {
			cout << 0 << endl;
			continue;
		}
		
		ll ans = d[a + b][a];
		if (ans <= 0) ans = 1;

		ll p = n - a - b;

		if (p > 0 && p < n) {
			ans *= binom(n, p);
			ans %= mod;
		}
		

		ans *= f[n];
		ans %= mod;

		cout << ans << endl;

	}
	
}

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