poj 3122 Pie

#include <iostream>        //二分查找
#include <algorithm>
#include <math.h>
using namespace std;
# define pi 3.1415926535898
#define  precisions 1e-5
bool cmp(const double& a,const double& b)    
{
    return a>b;
}
int piece(double total,double a)
{
    int m=0;
    while(total>=a)
    {
        m++;
        total-=a;
    }
    return m;
}
int main()
{
    int c,n,f,i,r;double pie[10010];
    scanf("%d",&c);
    while(c--)
    {
        scanf("%d%d",&n,&f);
        int max=0;
        for(i=0;i<n;++i)
        {
            scanf("%d",&r);
            if(max<r)
                max=r;
            pie[i]=pi*r*r;
        }
        sort(pie,pie+n,cmp);
        double begin=0,end=pi*max*max,mid;
        while(end-begin>precisions)
        {
            mid=(begin+end)/2;
            int count=0;
            for(i=0;i<n;++i)
            {
                if(pie[i]<mid)
                    break;
                count+=piece(pie[i],mid);
                if(count>=f+1)
                    break;
            }
            if(count>=f+1)
                begin=mid;
            else 
                end=mid;
        }
        printf("%.4f\n",mid);
    }
    return 0;
}