Submission #4347936

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Source Code Expand

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <vector>
#include <string>
#include <array>
#include <queue>
#include <deque>
#include <set>
#include <list>
#include <map>
#include <stack>
#include <utility>
#include <algorithm>
#include <numeric>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <cstring>
#include <climits>
#include <bitset>
#include <random>
#include <functional>
#include <sstream>
#include <iomanip>

using namespace std;

#define rep(i, n) for(int i=0; i<(n); i++)
#define FOR(i, m, n) for(int i=(m);i<(n);i++)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(),(x).end()
#define SORT(x) sort((x).begin(),(x).end())
#define REVE(x) reverse((x).begin(),(x).end())
#define mp make_pair
#define pb push_back

typedef vector<int> VI;
typedef vector<string> VS;
typedef vector<vector<int>> VVI;
typedef pair<int, int> PII;
typedef long long LL;

int main() {
	int n; cin >> n;
	VI c(n); rep(i, n)cin >> c[i];
	SORT(c);

	int x = 0, y = 0;
	do {
		vector<bool> b(n);
		rep(i, n - 1)FOR(j, i + 1, n)
			if (c[j] % c[i] == 0)b[j] = b[j] ? false : true;
		rep(i, n)if (!b[i])x++;
		y++;
	} while (next_permutation(all(c)));

	printf("%.12f\n", (double)x / y);
}

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