POJ 1491

 1 #include<iostream>
 2 #include<cmath>
 3 #include<iomanip>
 4 #define MAXN 50
 5 using namespace std;
 6 
 7 int _m[MAXN];
 8 int gcd(int a,int b);
 9 int main()
10 {
11     //freopen("acm.acm","r",stdin);
12     int n;
13     int i;
14     int j;
15     double sum_all;
16     double sum;
17     while(cin>>n,n)
18     {
19         sum = 0;
20         sum_all = 0;
21         for(i = 0; i < n; ++ i)
22         {
23             cin>>_m[i];
24         }
25         for(i = 0; i < n; ++ i)
26         {    
27             for(j = i+1; j < n; ++ j)
28             {
29                 if(gcd(_m[i],_m[j]) == 1)
30                 {
31                     ++ sum;
32                 }
33                 ++ sum_all;
34             }
35         }
36         if(sum == 0)
37         {
38             cout<<"No estimate for this data set."<<endl;
39             continue;
40         }
41          
42         cout<<setiosflags(ios::fixed)<<setprecision(6)<<sqrt(((sum_all*6.0)/sum))<<endl;
43     }
44 
45 }
46 
47 int gcd(int a,int b)
48 {
49     if(b == 0)
50         return a;
51     return gcd(b,a%b);
52 }