Submission #871121

#	Time	Username	Problem	Language	Result	Execution time	Memory
871121		MinaRagy06	NoM (RMI21_nom)	C++17	100 / 100	211 ms	63608 KiB

Main

#include <bits/stdc++.h>
using namespace std;
typedef int64_t ll;

const int mod = 1e9 + 7;
struct mint {
	int v;
	mint(long long x) {
		if (x >= mod) x %= mod;
		v = x;
	}
	mint() {v = 0;}
	mint& operator+=(mint b) {
		if ((v += b.v) >= mod) {
			v -= mod;
		}
		return *this;
	}
	mint& operator-=(mint b) {
		if ((v -= b.v) < 0) {
			v += mod;
		}
		return *this;
	}
	mint& operator*=(mint b) {
		v = 1ll * v * b.v % mod;
		return *this;
	}
	mint power(mint a, int b) {
		mint ans = 1;
		while (b) {
			if (b & 1) {
				ans *= a;
			}
			a *= a, b >>= 1;
		}
		return ans;
	}
	mint& operator/=(mint b) {
		v = 1ll * v * power(b, mod - 2).v % mod;
		return *this;
	}
	friend mint operator+(mint a, mint b) {
		return a += b;
	}
	friend mint operator-(mint a, mint b) {
		return a -= b;
	}
	friend mint operator*(mint a, mint b) {
		return a *= b;
	}
	friend mint operator/(mint a, mint b) {
		return a /= b;
	}
	friend istream& operator>>(istream &is, mint a) {
		return is >> a.v;
	}
	friend ostream& operator<<(ostream &os, mint a) {
		return os << a.v;
	}
};
const int N = 4005;
mint dp[N][N], fact[N], inv[N];
mint nCr(int n, int r) {
	return fact[n] * inv[n - r] * inv[r];
}
mint nPr(int n, int r) {
	return fact[n] * inv[n - r];
}
int main() {
	ios_base::sync_with_stdio(0), cin.tie(0);
	fact[0] = 1;
	for (int i = 1; i < N; i++) {
		fact[i] = fact[i - 1] * i;
	}
	inv[N - 1] = 1 / fact[N - 1];
	for (int i = N - 2; i >= 0; i--) {
		inv[i] = inv[i + 1] * (i + 1);
	}
	int n, m;
	cin >> n >> m;
	int a[m]{};
	for (int i = 0; i < 2 * n; i++) {
		a[i % m]++;
	}
	dp[m][0] = 1;
	for (int i = m - 1; i >= 0; i--) {
		for (int j = 0; j <= 2 * n; j++) {
			for (int k = 0; k <= min(j, a[i]); k++) {
				dp[i][j] += dp[i + 1][a[i] - k + j - k] * nPr(a[i], k) * nCr(j, k);
			}
		}
	}
	cout << dp[0][0] * fact[n] * mint().power(2, n) << '\n';
	return 0;
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 13 / 13
• Subtask 4: 18 / 18
• Subtask 5: 48 / 48