poj1491

简单题

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;

#define maxn 55

int n;
int f[maxn];

int gcd(int a, int b)
{
    if (b > 0)
        return gcd(b, a % b);
    return a;
}

void input()
{
    for (int i = 0; i < n; i++)
        scanf("%d", &f[i]);
}

void work()
{
    int numerator = 0;
    for (int i = 0; i < n; i++)
        for (int j = i + 1; j < n; j++)
            if (gcd(f[i], f[j]) == 1)
                numerator++;
    if (numerator == 0)
    {
        printf("No estimate for this data set.\n");
        return;
    }
    printf("%.6f\n", sqrt(n * (n - 1) * 3.0 / numerator));
}

int main()
{
//    freopen("t.txt", "r", stdin);
    while (scanf("%d", &n), n)
    {
        input();
        work();
    }
    return 0;
}