Submission #1177936

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
typedef pair<int, int> P;
typedef long long ll;

// 約数の列挙
vector<int> divisor(int n) {
    vector<int> res;
    for (int i=1;i*i<=n;++i) {
        if (n%i == 0) {
            res.push_back(i);
            if (i != n/i) res.push_back(n/i);
        }
    }
    return res;
}

int main() {
    int N;
    cin >> N;
    vector<int> C(N);
    rep(i, N) cin >> C[i];

    double ans=0;
    rep(i, N) {
        vector<int> t = divisor(C[i]);
        bitset<101> flag;
        rep(j, t.size()) {
            rep(k, N) {
                if (i == k) continue;
                if (t[j] == C[k] && !flag[k]) { flag[k]=1; }
            }
        }
        int S = flag.count();
        if (S%2) ans += 1.0/2.0;
        else {
            ans += (double)((S+1)-(S/2))/(S+1);
        }
    }

    printf("%.10f\n", ans);
}

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