Light Bulb ZOJ - 3203 三分

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#include <iostream>
#include <cmath>
#include <cstdio>
#include <algorithm>

using namespace std;

const double eps=1e-9;

int sgn(double x)
{
    if(fabs(x)<eps)
        return 0;
    if(x<0)
        return -1;
    else
        return 1;
}

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

double three_search(double l,double r)
{
    while(sgn(r-l)>0)
    {
        double lmid;
        double rmid;
        lmid=l+(r-l)/3;
        rmid=r-(r-l)/3;
        if(f(lmid)>=f(rmid))
            r=rmid;
        else
            l=lmid;
    }
    return f(l);
}
int main()
{
    int n;
    cin>>n;
    while(n--)
    {
        cin>>H>>h>>D;
        double ans;
        ans=three_search((H-h)*D/H,D);
        printf("%.3lf\n",ans);
    }
    return 0;
}