Submission #376176

#	Time	Username	Problem	Language	Result	Execution time	Memory
376176		YJU	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	17 ms	23020 KiB

kangaroo

#include<bits/stdc++.h>
#pragma GCC optimize("unroll-loops,no-stack-protector,Ofast")
using namespace std;
typedef long long ll;
typedef pair<ll,ll> pll;
typedef long double ld;
const ll N=2e3+5;
const ll MOD=1e9+7;
const ll INF=(1LL<<61);
const ld pi=acos(-1);
#define REP(i,n) for(int i=0;i<n;++i)
#define REP1(i,n) for(int i=1;i<=n;++i)
#define pb push_back
#define mp make_pair
#define X first
#define Y second
#define lwb lower_bound
#define SZ(_a) (ll)_a.size()

ll n,s,t,dp[N][N];

int main(){
	ios_base::sync_with_stdio(0);cin.tie(0);
	cin>>n>>s>>t;
	dp[1][1]=1;
	for(int i=2;i<=n;i++){
        for(int j=1;j<=i;j++){
			if(i==s||i==t){
                dp[i][j]=dp[i-1][j-1]+dp[i-1][j];
			}else{
				dp[i][j]=(dp[i-1][j+1]*j+dp[i-1][j-1]*(j-(i>s)-(i>t)))%MOD;
			}
			if(dp[i][j]>=MOD)dp[i][j]-=MOD;
		}
	}
	cout<<dp[n][1]<<"\n";
	return 0;
}
/*
*/

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