Submission #830944

#	Time	Username	Problem	Language	Result	Execution time	Memory
830944		12345678	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	18 ms	23000 KiB

kangaroo

#include <bits/stdc++.h>

using namespace std;

#define ll long long

const ll nx=2e3+5, mod=1e9+7;
ll dp[nx][nx], n, s, e, k=2;

int main()
{
    cin.tie(NULL)->sync_with_stdio(false);
    cin>>n>>s>>e;
    dp[1][1]=1;
    for (ll i=1; i<=n; i++)
    {
        if (i==s||i==e)
        {
            for (ll j=1; j<i; j++)
            {
                dp[i][j+1]=(dp[i][j+1]+dp[i-1][j])%mod;
                dp[i][j]=(dp[i][j]+dp[i-1][j])%mod;
            }
            k--;
            continue;
        }
        for (ll j=1; j<i; j++)
        {
            dp[i][j+1]=(dp[i][j+1]+dp[i-1][j]*(j+1+k-2))%mod;
            dp[i][j-1]=(dp[i][j-1]+dp[i-1][j]*(j-1))%mod;
        }
    }
    cout<<dp[n][1];
}

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