Submission #1556650

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Source Code Expand

#define _CRT_SECURE_NO_WARNINGS
#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <vector>

using namespace std;

array<int, 100> C;
vector<int> dev;

// 約数
void devisor(vector<int> &dev, int k)
{
    int n;
    int i = 2;

    n = k;

    while (i <= sqrt(n))
    {
        if (n % i == 0) {
            dev.push_back(i);
            if (i != (n / i)) {
                dev.push_back(n / i);
            }
        }

        i++;
    }

    vector<int>::iterator it = find(dev.begin(), dev.end(), n);
    size_t ix = distance(dev.begin(), it);
    if (ix == dev.size()) dev.push_back(n);

    sort(dev.begin(), dev.end());
}

int main()
{
    int N;
    if (scanf("%d", &N) < 1) return 0;

    for (int i = 0; i < N; i++) if (scanf("%d", &C[i]) < 1) return 0;

    double ans = 0.0L;
    for (int i = 0; i < N; i++)
    {
        dev.clear();
        dev.shrink_to_fit();
        devisor(dev, C[i]);

        int cnt = 0;
        for (int j = 0; j < N; j++)
        {
            for (int k = 0; k < dev.size(); k++)
            {
                if (C[j] == dev[k])
                {
                    cnt++;
                    break;
                }
            }
        }

        // 約数 自分自身は除き、自分自身と同じ数は含める
        cnt--;

        if (cnt % 2 == 1) ans += 0.5;
        else
        {
            double tmp1 = cnt + 2.0;
            double tmp2 = 2.0 * cnt + 2.0;
            ans += tmp1 / tmp2;
        }
    }

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

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