HDU 2438 Turn the corner 三分法

Turn the corner

Time Limit: 3000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 1767 Accepted Submission(s): 664

Problem Description
Mr. West bought a new car! So he is travelling around the city.

One day he comes to a vertical corner. The street he is currently in has a width x, the street he wants to turn to has a width y. The car has a length l and a width d.

Can Mr. West go across the corner?



Input
Every line has four real numbers, x, y, l and w.

Proceed to the end of file.
Output
If he can go across the corner, print "yes". Print "no" otherwise.
Sample Input

10 6 13.5 4
10 6 14.5 4

只要 (l*sin(a)+d/cos(a)-x)/tan(a) < y 即可通过

/*
函数先增后减 找到最大值 三分 
*/
#include<iostream>
#include<stdio.h>
#include<cmath>
using namespace std;

#define PI acos(-1.0)
double x,y,l,d;
double f(double a)
{
    return (l*sin(a)+d/cos(a)-x)/tan(a);
}

int  main(){
    
    double low,high,mid,mmid;
    while(scanf("%lf%lf%lf%lf",&x,&y,&l,&d)!=EOF)
    {
        low=0;high=PI/2;
        if(x<d||y<d) {
            printf("no\n");
            continue;
        }
        
        while(high-low>1e-7)
        {
            mid=(low+high)/2;
            mmid=(mid+high)/2;
            if(f(mid)>f(mmid))
                high=mmid+1e-9;
            else
                low=mid-1e-9;
        }
        if(f(mid)<y)
            printf("yes\n");
        else
            printf("no\n");
    }
    
    return 0;
}