ZOJ Light Bulb - 3203

题意：人左右走动，求影子L的最长长度。

思路：三分人在D上的位置。注意影子长=D-x+H-(H-h)*D/x。

#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<memory.h>
#include<string.h>
#include<algorithm>
#include<cmath>
#define clc(a,b) memset(a,b,sizeof(a))
typedef long double ld;
typedef long long ll;
const int N = 30;
const double eps=1e-9;
const int inf=-100000;
const int maxn=1e5+10;
const double Pi=acos(-1);
using namespace std;

double H,h,D;

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

double solve(double l,double r)
{
    //cout<<"11"<<endl;
    double mid,midmid;
    double d1,d2;
    while(r-l>=eps)
    {
        mid=(l+r)/2;
        midmid=(mid+r)/2;
        d1=calc(mid);
        d2=calc(midmid);
        if(d1>=d2)
            r=midmid;
        else
            l=mid;
    }
    return d1;
}

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%lf%lf%lf",&H,&h,&D);
        printf("%.3lf\n",solve((H-h)*D/H,D));
    }
    return 0;
}