【三分法】hdu2438 Turn the corner

#include<cstdio>
#include<cmath>
#include<iostream>
#define PI 3.14159
using namespace std;

double x,y,l,d;

double pd(double a)
{
    return sin(a)*l+d/cos(a)-y*tan(a);
}

int main()
{
    while(scanf("%lf%lf%lf%lf",&x,&y,&l,&d)!=EOF)
    {
        double lm,rm,le=0.0,r=PI/2;
        while(fabs(r-le)>1e-6)
        {
            lm=(le*2.0+r)/3.0;
            rm=(le+r*2.0)/3.0;
            if(pd(lm)>pd(rm)) r=rm;
            else le=lm;
        }
        if(pd(le)<=y)
            printf("yes\n");
        else
            printf("no\n");
    }
}