HDUOJ--Strange fuction

Strange fuction

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 2098    Accepted Submission(s): 1577

Problem Description

Now, here is a fuction:
  F(x) = 6 * x^7+8*x^6+7*x^3+5*x^2-y*x (0 <= x <=100)
Can you find the minimum value when x is between 0 and 100.

 

Input

The first line of the input contains an integer T(1<=T<=100) which means the number of test cases. Then T lines follow, each line has only one real numbers Y.(0 < Y <1e10)

 

Output

Just the minimum value (accurate up to 4 decimal places),when x is between 0 and 100.

 

Sample Input

2 100 200

 

Sample Output

-74.4291 -178.8534

 

Author

Redow

 

Recommend

lcy

http://acm.hdu.edu.cn/showproblem.php?pid=2899

代码：

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
double y;
double sum(double x)
{
    return 6*pow(x,7)+8*pow(x,6)+7*pow(x,3)+5*pow(x,2)-y*x;
}
double func(double x)
{
    return 42*pow(x,6)+48*pow(x,5)+21*x*x+10*x-y;
}
int main()
{
    int t;
    double mid,left,right;
    cin>>t;
    while(t--)
    {
        scanf("%lf",&y);
        if(func(100)>0)
        {
        left=0.0,right=100.0;
        while(right-left>1e-8)
        {
          mid=(right+left)/2.0;
          if(func(mid)>0.0)
                right=mid;
        else
            if(func(mid)<0.0)
                left=mid;
            else
                break;
        }
        printf("%.4lf
",sum(mid));
        }
        else
            printf("%.4lf
",sum(100.0));
    }
    return 0;
}