Submission #1117968

#	Time	Username	Problem	Language	Result	Execution time	Memory
1117968		AtabayRajabli	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	25 ms	23120 KiB

kangaroo

#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define int long long
using namespace std;

const int sz = 2e3 + 4, mod = 1e9 + 7;
int n, s, f, dp[sz][sz];

signed main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    
    cin >> n >> s >> f;
    
    int fixed = 0;
    dp[1][1] = 1;
    for(int i = 1; i <= n; i++)
    {
        if(i == s || i == f) fixed++;
        for(int j = 1; j <= i; j++)
        {
            if(i == s || i == f) 
            {
                dp[i][j] += dp[i - 1][j - 1];
                dp[i][j] %= mod;

                dp[i][j] += dp[i - 1][j];
                dp[i][j] %= mod;
            }
            else
            {
                dp[i][j] += dp[i - 1][j - 1] * (j - fixed) % mod;
                dp[i][j] %= mod;

                dp[i][j] += dp[i - 1][j + 1] * j % mod;
                dp[i][j] %= mod;
            }
        }
    }
    cout << dp[n][1];
}

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