Submission #524151

#	Time	Username	Problem	Language	Result	Execution time	Memory
524151		two_sides	NoM (RMI21_nom)	C++17	100 / 100	95 ms	452 KiB

Main

#include <bits/stdc++.h>

using namespace std;

const int N = 4005;
const int MOD = 1e9 + 7;

int dp[2][N], fac[N], inv[N];

int add(int x, int y) {
    return (x += y) >= MOD ? x - MOD : x;
}

int sub(int x, int y) {
    return (x -= y) < 0 ? x + MOD : x;
}

int mul(int x, int y) {
    return (long long)x * y % MOD;
}

int bin(int n, int k) {
    if (n < k) return 0;
    return mul(fac[n], mul(inv[k], inv[n - k]));
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    int n, m; cin >> n >> m;
    fac[0] = inv[0] = inv[1] = 1;
    for (int i = 2; i < N; i++)
        inv[i] = MOD - mul(MOD / i, inv[MOD % i]);
    for (int i = 1; i < N; i++) {
        fac[i] = mul(fac[i - 1], i);
        inv[i] = mul(inv[i - 1], inv[i]);
    }
    dp[0][0] = 1;
    for (int i = 0; i < m; i++) {
        int l = (2 * n - i - 1) / m + 1;
        memset(dp[~i & 1], 0, sizeof dp[~i & 1]);
        for (int j = 0; j <= n; j++)
            for (int k = 0; k * 2 <= l && k <= j; k++)
                dp[~i & 1][j] = add(dp[~i & 1][j],
                mul(dp[i & 1][j - k], mul(bin(j, k),
                mul(fac[l], inv[l - 2 * k]))));
    }
    int res = 0;
    for (int i = 0; i <= n; i++) {
        int cur = mul(dp[m & 1][i], mul
        (bin(n, i), fac[2 * n - 2 * i]));
        if (i & 1) res = sub(res, cur);
        else res = add(res, cur);
    }
    cout << res;
}

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