Submission #3980904

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Source Code Expand

#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

const double PI = 3.1415926535897932384626433832795;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { -1, 0, 1, 0 };

int gcd(int x, int y) { return y ? gcd(y, x % y) : abs(x); }
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : abs(x); }
int lcm(int x, int y) { return x / gcd(x, y) * y; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	int n;
	cin >> n;

	vector<int> c(n);
	for (auto &v : c) {
		cin >> v;
	}
	sort(begin(c), end(c));

	double ans = 0;
	for (int i = 0; i < n; i++) {
		int s = 0;
		for (int j = 0; j < n; j++) {
			if (i == j) {
				continue;
			}

			if (c[i] % c[j] == 0) {
				s++;
			}
		}
		ans += (s % 2 == 1 ? 0.5 : (s + 2.0) / (2 * s + 2.0));
	}

	printf("%.12lf\n", ans);
	return 0;
}

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