Submission #6005007

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Source Code Expand

// {{{
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
// }}}

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;

static constexpr int mod = (int)1e9 + 7;
static constexpr int inf = 100100100;
static constexpr ll linf = 1e18;
static constexpr double eps = 1e-9;
static constexpr double pi = 3.14159265359;

#define rep(i, n) for (ll i = 0; i < n; ++i)
#define rrep(i, n) for (ll i = n; i >= 0; --i)
#define all(c) begin(c), end(c)
#define rall(c) rbegin(c), rend(c)
#define pb push_back
#define ist insert
#define fst first
#define snd second


int main() {
    // cin.tie(0);
    // ios_base::sync_with_stdio(false);
    ll N;
    cin >> N;
    vector<ll> C;
    rep (i, N) {
        ll c;
        cin >> c;
        C.pb(c);
    }
    map<ll, vector<ll>> M;
    rep (i, N) {
        M[i];
        rep (j, N) {
            if (i == j) continue;
            if (C[i] % C[j] == 0) {
                M[i].pb(C[j]);
            }
        }
    }
    double ans = 0;
    for (auto it : M) {
        if (it.snd.size() % 2 == 0) {
            ans += (it.snd.size() + 2.) / (2. * it.snd.size() + 2.);
        } else {
            ans += 0.5;
        }
    }
    printf("%.16lf\n", ans);
}

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