poj 1491 Pi

#include <iostream>            //水题
#include <cmath>
using namespace std;
int  gcd(int  x,int  y)   
{   
    if (x==0||y==0)  
        return  max(x,y);
    int  i=0,j=0; 
    while (x&1==0)
    {
        ++i;
        x=x>>1;
    }
    while (y&1==0)
    {
        ++j;
        y=y>>1;
    }
    i=min(i,j);  
    while(1)
    {        
        if(x<y)
            swap(x,y);
        x-=y;
        if(x==0)
            return y<<i;
        while(x&1==0)
        {
            x=x>>1;
        }
    }   
}
int main()
{
    int n,data[100],s;
    while(cin>>n&&n)
    {
        for(int i=0;i<n;++i)
            cin>>data[i];
        s=0;
        for(int i=0;i<n;++i)
        {
            for(int j=i+1;j<n;++j)
                if(gcd(data[i],data[j])==1)
                    s++;
        }
        if(s==0)
            printf("No estimate for this data set.\n");
        else
            printf("%.6f\n",sqrt(3.0*n*(n-1)/s));
    }
    return 0;
}