POJ 1491

#include<iostream>
#include<cmath>
#include<iomanip>
#define MAXN 50
using namespace std;

int _m[MAXN];
int gcd(int a,int b);
int main()
{
    //freopen("acm.acm","r",stdin);
    int n;
    int i;
    int j;
    double sum_all;
    double sum;
    while(cin>>n,n)
    {
        sum = 0;
        sum_all = 0;
        for(i = 0; i < n; ++ i)
        {
            cin>>_m[i];
        }
        for(i = 0; i < n; ++ i)
        {    
            for(j = i+1; j < n; ++ j)
            {
                if(gcd(_m[i],_m[j]) == 1)
                {
                    ++ sum;
                }
                ++ sum_all;
            }
        }
        if(sum == 0)
        {
            cout<<"No estimate for this data set."<<endl;
            continue;
        }
         
        cout<<setiosflags(ios::fixed)<<setprecision(6)<<sqrt(((sum_all*6.0)/sum))<<endl;
    }

}

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

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