poj 3122 pie(二分搜索)

#include <iostream>
#include <cmath>
using namespace std;
const double PI=acos(-1.0); //3.14过不了 
double area[10005];
double max_area;
int n,f;
int OK(double k)
{	int i,Count=0;
	for(i=0;i<n;i++)
		Count+=floor(area[i]/k);
	return Count>=f+1;
	
}
double binary()
{
	double left=0,right=max_area,middle;
	while(left<right&&(right-left)>=10e-6)
	{		
		middle=(left+right)/2;
		if(!OK(middle)) right=middle;
		else left=middle;
	}
	return middle;
}
int main(int argc, char *argv[])
{
	int t,i,j;
	double r;
	cin>>t;
	while(t--)
	{
		cin>>n>>f;
		for(max_area=-1,i=0;i<n;i++)
			{cin>>r; area[i]=PI*r*r; max_area=max(max_area,area[i]); }
		printf("%.4lf\n",binary());	
	} 
	return 0;
}