Submission #797825

#	Time	Username	Problem	Language	Result	Execution time	Memory
797825		amirhoseinfar1385	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	814 ms	85876 KiB

kangaroo

#include<bits/stdc++.h>
using namespace std;
const int maxn=2000+10;
int mod=1e9+7;
long long pd[maxn][maxn];
int n,s,e;

int ww(long  long a){
	a%=mod;
	return a;
}

void calpd(){
	pd[1][1]=1;
	pd[2][1]=0;
	pd[2][2]=1;
	for(int i=3;i<=n;i++){
		if((i&1)==0){
			for(int j=1;j<=i;j++){
				pd[i][j]=pd[i][j-1]+pd[i-1][i-j+1]+pd[i-1][j-1];
				pd[i][j]=ww(pd[i][j]);
//				cout<<i<<" "<<j<<" "<<pd[i][j]<<"\n";
			}
		}
		else{
			for(int j=2;j<=i;j++){
				pd[i][j]=pd[i][j-1]+mod-pd[i-1][j-1]+pd[i-1][i-j+1];
				pd[i][j]=ww(pd[i][j]);
//				cout<<i<<" "<<j<<" "<<pd[i][j]<<"\n";
			}
		}
	}
}
map<pair<pair<int,int>,int>,int>mp;

long long caldp(int fn,int i,int j,int k){
	long long res=0;
	if(fn==0){
		if(i==0&&j==0&&k==0){
			return 1;
		}
		return 0;
	}
	if(mp.count(make_pair(make_pair(fn,i),k))!=0){
		return mp[make_pair(make_pair(fn,i),k)];
	}
	res+=caldp(fn-1,i+1,j,k);
	if(k==0){
		res+=pd[j+i+fn][j+1];
		res+=caldp(fn-1,i,j,k^1);
	}
	else{
		res+=pd[fn+i+j][fn+i];
		res+=mod-caldp(fn-1,i,j,k^1);
	}
	res=ww(ww(res));
	 mp[make_pair(make_pair(fn,i),k)]=res;
	return res;
}

int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>s>>e;
	if(s>e){
		swap(s,e);
	}
	calpd();
	int res=ww(caldp(e-s,s-1,n-e,0)+caldp(e-s,s-1,n-e,1));
	s++;
	res+=mod-ww(caldp(e-s,s-1,n-e,0)+caldp(e-s,s-1,n-e,1));
	res=ww(res);
	cout<<res<<"\n";
	return 0;
}

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