Submission #1237503

#	Time	Username	Problem	Language	Result	Execution time	Memory
1237503		chikien2009	Kangaroo (CEOI16_kangaroo)	C++20	100 / 100	14 ms	23112 KiB

kangaroo

#include <bits/stdc++.h>

using namespace std;

void setup()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
}

int n, a, b;
long long c, f[2002][2002], mod = 1e9 + 7;

int main()
{
    setup();

    cin >> n >> a >> b;
    f[0][0] = 1;
    for (int i = 1; i <= n; ++i)
    {
        c += (i == a || i == b);
        for (int j = 1; j <= i; ++j)
        {
            if (i == a || i == b)
            {
                f[i][j] = (f[i - 1][j] + f[i - 1][j - 1]) % mod;
            }
            else
            {
                f[i][j] = (f[i - 1][j - 1] * (j - c) + f[i - 1][j + 1] * j) % mod;
            }
        }
    }
    cout << f[n][1];
    return 0;
}

• Subtask 1: 6 / 6
• Subtask 2: 30 / 30
• Subtask 3: 15 / 15
• Subtask 4: 49 / 49