zoj 3203 Light Bulb，三分之二的基本问题

Light Bulb

name=light_bulb_1037_ddd01.gif" >

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

3
2 1 0.5
2 0.5 3
4 3 4

Sample Output

1.000
0.750
4.000

注意精度这题最低是eps = 1e-8;

#include<cstdio>

const double eps = 1e-8;

double H, h, D;
double f(double x)
{
    return H-(H-h)*D/x + D-x;
}
int main()
{
    int t;
    scanf("%d", &t);
    while(t--)
    {
        scanf("%lf%lf%lf", &H, &h, &D);
        double l = D-h*D/H, r = D;
        double ans = -100;
        while(l+eps<r)
        {
            double m1 = l + (r-l)/3;
            double m2 = r - (r-l)/3;
            if(f(m1)<f(m2)) l = m1, ans = f(m2);
            else r = m2, ans = f(m1);
        }
        printf("%.3f\n", ans);
    }
    return 0;
}

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