Submission #1611830

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Source Code Expand

# include <iostream>
# include <algorithm>
# include <vector>
# include <string>
# include <set>
# include <map>
# include <cmath>
# include <iomanip>
# include <functional>
# include <utility>
# include <stack>
# include <queue>
# include <list>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
constexpr long long MOD = 1000000000 + 7;
constexpr long long INF = 100000000000000;
const double PI = acos(-1);

int main() {
	int n, d, x, y;
	cin >> n >> d >> x >> y;
	if (!(x%d == 0 && y%d == 0)) {
		cout << 0.0 << endl;
		return 0;
	}
	x /= d;
	y /= d;
	x = abs(x);
	y = abs(y);
	if (x + y > n) {
		cout << 0.0 << endl;
		return 0;
	}
	if ((n - x - y) % 2 == 1) {
		cout << 0.0 << endl;
		return 0;
	}
	double ans = 1;
	if (x + y == n) {
		for (int i = n; i > x; i--) {
			ans *= i;
			ans /= (i - x);
		}
		for (int i = 0; i < n; i++) {
			ans /= 4;
		}
		cout << fixed << setprecision(12) << ans << endl;
		return 0;
	}
	else {
		for (int i = x + y + (n - x - y) / 2; i > x; i--) {
			ans *= i;
			ans /= (i - x);
		}
		ans *= ((n - x - y) / 2 + 1)*((n - x - y) / 2 + 1);
		for (int i = 0; i < n; i++) {
			ans /= 4;
		}
		cout << fixed << setprecision(12) << ans << endl;
	}
}

Submission Info

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