Submission #1298307

#	Time	Username	Problem	Language	Result	Execution time	Memory
1298307		nguyenletrung	Kangaroo (CEOI16_kangaroo)	C++20	100 / 100	26 ms	23052 KiB

kangaroo

#include<bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define ins insert
#define pb push_back
#define foru(i,a,b) for(int i=a;i<=b;i++)
#define ford(i,a,b) for(int i=a;i>=b;i--)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define int ll
using namespace std;

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

signed main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
//	freopen(".inp","r",stdin);
//	freopen(".out","w",stdout);
	cin>>n>>cs>>cf;
	
	dp[1][1]=1;
	
	for(int i=1;i<=n;i++)
	{
		if(i==cs||i==cf) cnt++;
		for(int j=1;j<i;j++)
		{
			if(i==cs||i==cf)
			{
				dp[i][j+1]+=dp[i-1][j];
				dp[i][j+1]%=mod;
				
				dp[i][j]+=dp[i-1][j];
				dp[i][j]%=mod;
			}
			else
			{
				dp[i][j+1]+=(j+1-cnt)*dp[i-1][j]%mod;
				dp[i][j+1]%=mod;
				
				dp[i][j-1]+=(j-1)*(dp[i-1][j])%mod;
				dp[i][j-1]%=mod;
			}
		}
	}
	
	cout<<(dp[n][1]%mod+mod)%mod;
}
/*
em thi cho du co khoc
cung se den ngay phai quen
thien duong van cho ngay em den
*/

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