Submission #316145

#	Time	Username	Problem	Language	Result	Execution time	Memory
316145		vipghn2003	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	37 ms	14208 KiB

kangaroo

#include<bits/stdc++.h>

using namespace std;

const int N=2005;
const int mod=1e9+7;
int n,cs,cf,dp[N][N];

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>n>>cs>>cf;
    if(cs>cf) swap(cs,cf);
    dp[1][0]=1;
    for(int i=1;i<=n;i++)
    {
        for(int j=0;j<=i;j++)
        {
            if(i==cs||i==cf)
            {
                 dp[i+1][j]=(dp[i+1][j]+dp[i][j])%mod;
                 if(j) dp[i+1][j-1]=(dp[i+1][j-1]+1ll*dp[i][j]*j%mod)%mod;
                 continue;
            }
            dp[i+1][j+1]=(dp[i+1][j+1]+dp[i][j])%mod;
            if(j)
            {
                dp[i+1][j-1]=(dp[i+1][j-1]+1ll*j*(j-1)%mod*dp[i][j]%mod);
                if(i>cs) dp[i+1][j-1]=(dp[i+1][j-1]+1ll*dp[i][j]*j%mod)%mod;
                if(i>cf) dp[i+1][j-1]=(dp[i+1][j-1]+1ll*dp[i][j]*j%mod)%mod;
            }
        }
    }
    cout<<dp[n][0];
}

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