Submission #1223780

#	Time	Username	Problem	Language	Result	Execution time	Memory
1223780		chaeryeong	Tents (JOI18_tents)	C++20	100 / 100	194 ms	98364 KiB

tents

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MOD = 1e9 + 7;
int add (int a, int b) {
	a += b; if (a >= MOD) a -= MOD;
	return a;
}
int sub (int a, int b) {
	a -= b; if (a < 0) a += MOD;
	return a;
}
int mul (int a, int b) {
	return (a * 1ll * b) % MOD;
}
int power (int a, int b) {
	if (!b) return 1;
	int u = power(a, b >> 1);
	u = mul(u, u);
	if (b & 1) u = mul(u, a);
	return u;
}
const int N = 5000;
int fact[N + 1], inv[N + 1];
int nCr (int a, int b) {
	return mul(fact[a], mul(inv[b], inv[a - b]));
}
int dp[N + 1][N + 1];
void solve () {
	fact[0] = 1;
	for (int i = 1; i <= N; i++) {
		fact[i] = mul(i, fact[i - 1]);
	}
	inv[N] = power(fact[N], MOD - 2);
	for (int i = N - 1; i >= 0; i--) {
		inv[i] = mul(i + 1, inv[i + 1]);
	}
	for (int i = 0; i <= N; i++) {
		dp[0][i] = 1;
	}
	for (int i = 1; i <= N; i++) {
		dp[i][0] = 1;
		for (int j = 1; j <= N; j++) {
			dp[i][j] = add(dp[i][j], dp[i - 1][j]);
			dp[i][j] = add(dp[i][j], mul(4 * j, dp[i - 1][j - 1]));
			if (i >= 2) {
				dp[i][j] = add(dp[i][j], mul(j * (i - 1), dp[i - 2][j - 1]));
			}
			if (j >= 2) {
				dp[i][j] = add(dp[i][j], mul(j * (j - 1) / 2, dp[i - 1][j - 2]));
			}
		}
	}
	int x, y; cin >> x >> y;
	cout << sub(dp[x][y], 1) << '\n';
}
signed main () {
	ios::sync_with_stdio(0); cin.tie(0);
	int tc = 1; //cin >> tc;
	while (tc--) solve();
}

• Subtask 1: 48 / 48
• Subtask 2: 52 / 52