ZOJ3203——Light Bulb(三分法)

Light Bulb

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Time Limit: 1 Second      Memory Limit: 32768 KB

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Compared to wildleopard's wealthiness, his brother mildleopard is rather poor. His house is narrow and he has only one light bulb in his house. Every night, he is wandering in his incommodious house, thinking of how to earn more money. One day, he found that the length of his shadow was changing from time to time while walking between the light bulb and the wall of his house. A sudden thought ran through his mind and he wanted to know the maximum length of his shadow.

Input

The first line of the input contains an integer T (T <= 100), indicating the number of cases.

Each test case contains three real numbers H, h and D in one line. H is the height of the light bulb while h is the height of mildleopard. D is distance between the light bulb and the wall. All numbers are in range from 10^-2 to 10³, both inclusive, and H - h>= 10^-2.

Output

For each test case, output the maximum length of mildleopard's shadow in one line, accurate up to three decimal places..

Sample Input

32 1 0.52 0.5 34 3 4

Sample Output

1.0000.7504.000

解析：当人从墙上刚有影子处向右一直走到墙的过程中，影子总长是关于墙上影子的凸函数

      三分墙上影子长。。。

代码：

#include<cstdio>#include<iostream>#include<algorithm>#include<cmath>using namespace std;const double lim=1e-6;double l,r;double H,h,d;int test;double calc(double x){    return x+(d*(h-x)/(H-x));}double sf(){    double m1,m2,mid;    do    {        mid=(r-l)/3;        m1=l+mid;m2=r-mid;        if(calc(m1)<calc(m2))l=m1; else r=m2;    }while(r-l>lim);    return calc(l);}void readdata(){    freopen("zoj3203.in","r",stdin);    freopen("zoj3203.out","w",stdout);    scanf("%d",&test);    while(test--)    {        scanf("%lf%lf%lf",&H,&h,&d);        l=0;r=h;        printf("%.3lf\n",sf());    }}int main(){    readdata();    return 0;}