zoj 3203

題目 http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=3366

三分法

#include<iostream>
#include<cmath>
#include<stdio.h>
using namespace std;

double H,h,D;

double cal(double x)
{
	return (h-x)*D/(H-x)+x;
}

int main()
{
	double left,right,m,mm;
	int t;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%lf%lf%lf",&H,&h,&D);
		left=0;
		right=h;
		while(left+1e-8<right)
		{
			m=(left+right)/2;
			mm=(m+right)/2;
			if(cal(m)>cal(mm))
			{
				right=mm;
			}
			else
			{
				left=m;
			}
		}
		printf("%.3lf\n",cal(left));
	}
	return 0;
}