Submission #1369120

#	Time	Username	Problem	Language	Result	Execution time	Memory
1369120		Newtonabc	Kangaroo (CEOI16_kangaroo)	C++20	100 / 100	20 ms	31852 KiB

kangaroo

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const ll MOD=1e9+7;
const int N=2e3+10;
ll dp[N][N];
int main(){
    int n,st,ed; cin>>n >>st >>ed;
    if(st>ed) swap(st,ed);
    dp[0][0]=1;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(i==st || i==ed){
                dp[i][j]+=dp[i-1][j];
                dp[i][j]+=dp[i-1][j-1];
                dp[i][j]%=MOD;
            }
            else{
                dp[i][j]+=dp[i-1][j-1]*(ll)(j-(i>st)-(i>ed));
                dp[i][j]+=dp[i-1][j+1]*(ll)(j);
                dp[i][j]%=MOD;
            }
        }
    }
    cout<<dp[n][1];
}

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