Cup HDU - 2289 二分

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const double eps=1e-9;
const double pie=3.1415926535;
int T;
double br,tr,H,v;
double getV(double h)
{
	double rr=(tr-br)*h/H+br; //相似三角形
	return pie*h*(br*br+rr*rr+br*rr)/3;
}
int main()
{
	cin>>T;
	while(T--)
	{
		cin>>br>>tr>>H>>v;
		//二分查找水的高度
		double l=0,r=H;
		while(r-l>eps)
		{
			double mid=(l+r)/2,curV=getV(mid);
			if(fabs(curV-v)<= eps)
				break;
			else if(curV>v)
				r=mid;
			else
				l=mid;
		}
		printf("%.6lf\n",l);
	}
	return 0;
}