Submission #1611816

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Source Code Expand

#include<deque>
#include<queue>
#include<vector>
#include<algorithm>
#include<iostream>
#include<set>
#include<cmath>
#include<tuple>
#include<string>
#include<chrono>
#include<functional>
#include<iterator>
#include<random>
#include<unordered_set>
#include<unordered_map>
#include<array>
#include<map>
#include<iomanip>
//<< setprecision(5)
using namespace std;
typedef long long int llint;
typedef long double lldo;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
#define dme cout<<-1<<endl;return 0
const int mod=1000000007;
const int big=5e8+10;
const long double pai=3.141592653589793238462643383279502884197;
const long double eps=1e-7;
template <class T,class U>void mineq(T& a,U b){if(a>b){a=b;}}
template <class T,class U>void maxeq(T& a,U b){if(a<b){a=b;}}
llint gcd(llint a,llint b){if(a%b==0){return b;}else return gcd(b,a%b);}
llint lcm(llint a,llint b){return a/gcd(a,b)*b;}
int main(void){
	int n,D;cin>>n>>D;
	int x,y,i;cin>>x>>y;
	if(x%D!=0){cout<<0<<endl;return 0;}
	if(y%D!=0){cout<<0<<endl;return 0;}
	x/=D;y/=D;x=abs(x);y=abs(y);//これでDは実質1
	if(x>n||y>n){cout<<0<<endl;return 0;}//そんなにとべない
	vector<lldo>xran(n+1);//想定道理に飛べた確率
	vector<lldo>yran(n+1);//想定道理に飛べた確率
	lldo dp[2017]={0};
	dp[1009]=1;
	for(i=0;i<n;i++){
		if(x%2==i%2){xran[i]=dp[x+1009];}
		if(y%2==i%2){yran[i]=dp[y+1009];}
		for(int j=i%2+2;j<=2015;j+=2){dp[j]=(dp[j-1]+dp[j+1])/2;}
	}
	if(x%2==i%2){xran[i]=dp[x+1009];}
	if(y%2==i%2){yran[i]=dp[y+1009];}
	//想定道理に飛ぶ確率終了
	lldo ans=0;
	for(i=0;i<=n;i++){//iはx方向に飛ぶ回数
		ans+=dp[1009-n+i*2]*xran[i]*yran[n-i];
	}
	cout<<setprecision(25)<<ans<<endl;
	return 0;
}

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