Submission #1261249

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Source Code Expand

#include "bits/stdc++.h"

#define ALL(a) (a).begin(),(a).end()
#define SORT(c) sort((c).begin(),(c).end())
#define DESCSORT(c) sort(c.begin(), c.end(), greater<int>())

using namespace std;

using LL = long long int;
using LD = long double;

using pii = pair<int, int>;
using pll = pair<LL, LL>;
using pdd = pair<double, double>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vl = vector<LL>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vd = vector<double>;
using vvd = vector<vd>;
using vs = vector<string>;
using vb = vector<bool>;
using vvb = vector<vb>;

const int INF = (1 << 30) - 1;
const LL INF64 = ((LL)1 << 62) - 1;
const double PI = 3.1415926535897932384626433832795;

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

int gcd(int x, int y) { return y ? gcd(y, x % y) : x; }
LL gcd(LL x, LL y) { return y ? gcd(y, x % y) : x; }

double solve(int n, vi 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));
	}
	return ans;
}

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

	int n;
	cin >> n;
	vi c(n);
	for (int i = 0; i < n; i++) {
		cin >> c[i];
	}
	SORT(c);

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

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