Submission #813223

#	Time	Username	Problem	Language	Result	Execution time	Memory
813223		Warinchai	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	62 ms	31656 KiB

kangaroo

#include<bits/stdc++.h>
using namespace std;
long long dp[2005][2005];
long long md=1e9+7;
int k;
int main(){
    int n,st,en;
    cin>>n>>st>>en;
    if(st==en){
        cout<<1;
    }
    dp[1][1]=1;
    for(int i=1;i<=n;i++){
        if(i==st||i==en){
            k++;
        }
        for(int j=1;j<=n;j++){
            if(i==st||i==en){
                dp[i][j+1]+=dp[i-1][j];
                dp[i][j]+=dp[i-1][j];
                dp[i][j]%=md;
                dp[i][j+1]%=md;

            }else{
                dp[i][j+1]+=dp[i-1][j]*(j+1-k);
                dp[i][j-1]+=dp[i-1][j]*(j-1);
                dp[i][j+1]%=md;
                dp[i][j-1]%=md;
            }
        }
    }
    cout<<dp[n][1];
   // cout<<"\n"<<k;
}

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