Submission #187916

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Source Code Expand

#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <deque>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cctype>
#include <cstring>
#include <ctime>
#include <iterator>
#include <bitset>
#include <numeric>
#include <list>
#include <iomanip>

#if __cplusplus >= 201103L
#include <array>
#include <tuple>
#include <initializer_list>
#include <unordered_set>
#include <unordered_map>
#include <forward_list>

#define cauto const auto&
#endif

using namespace std;


typedef long long LL;
typedef pair<int,int> pii;
typedef pair<LL,LL> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll, vLL;
typedef vector<vector<long long> > vvll, vvLL;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
	v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
	stringstream ss;
	ss << f;
	ss >> t;
}


#define REP(i,n) for(int i=0;i<int(n);++i)
#define ALL(v) (v).begin(),(v).end()
#define RALL(v) (v).rbegin(),(v).rend()
#define PB push_back


#define MOD 1000000007LL
#define EPS 1e-8


const double rat = 1e-100;
double cmb[1010][1010];


double solve(){
	LL n, d, x, y;
	cin >> n >> d >> x >> y;
	x = abs(x);
	y = abs(y);
	if(x % d || y % d){
		return 0.0;
	}
	x /= d;
	y /= d;
	if(x + y > n || (n - x - y) % 2){
		return 0.0;
	}

	double ans = 0.0;
	LL fr = (n - x - y) / 2;
	for(LL i = 0; i <= fr; ++i){
		LL k = n;
		double t = cmb[k][x + i];
		k -= x + i;
		t *= cmb[k][i];
		k -= i;
		t *= cmb[k][fr - i];
		ans += t;
	}
	ans = exp(log(ans) - 3.0 * log(rat) - n * log(4.0));

	return ans;
}


int main(){
	for(int i = 0; i < 1010; ++i){
		cmb[i][0] = rat;
		for(int j = 1; j <= i; ++j){
			cmb[i][j] = cmb[i - 1][j] + cmb[i - 1][j - 1];
		}
	}
	
	printf("%.15f\n", solve());
}

Submission Info

Judge Result