HDOJ1696 Pie【二分】

#include <stdio.h>
#include <math.h>
#define  PI 3.1415926535897931
double v[10001];
int n,f;
int test(double x)
{
    int s=0,i;
    for (i=0;i<n;i++)
        s+=(int)(v[i]/x);
    return s>=f?1:0;
}
int main()
{
    int cas,i,r;
    double sum,max;
    double left,right,mid;
    scanf("%d",&cas);
    while (cas--)
    {
        scanf("%d%d",&n,&f);
        f+=1;
        sum=0;
        for (i=0;i<n;i++)
        {
            scanf("%d",&r);
            v[i]=(double)PI*r*r;
            sum+=v[i];
        }
        max=sum/f;
        left=0.0;
        right=max;
        while ((right-left)>1e-6)
        {
            mid=(left+right)/2.0;            
            if (test(mid))
                left=mid;
            else
                right=mid;
        }
        printf("%.4lf\n",mid);
    }
    return 0;
}