HDU 2899 Strange fuction

Strange fuction
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 11746 Accepted Submission(s): 7841

Problem Description
Now, here is a fuction:
F(x) = 6 * x^7 +8* x^6 + 7x^ 3+5x^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

这个题可以三分求单调性，也可以求导再进行计算。

#include<iostream>
#include<cstdio>
using namespace std;
double F(double x,double y)
{
	return 6*pow(x,7)+8*pow(x,6)+7*pow(x,3)+5*pow(x,2)-y*x;
}
double f(double x)//易知导函数单调递增，则原函数先减后增；
{
	return 42*pow(x,6)+48*pow(x,5)+21*pow(x,2)+10*x;
}
int main()
{
	int t;
	double y,l,h,mid;
	cin>>t;
	while(t--)
	{
		cin>>y;
		l=0.0;h=100.0;
		while(h-l>1e-7)
		{
			mid=(l+h)/2;
			if(f(mid)<y) l=mid;
			else h=mid;
		}
		printf ("%.4lf\n",F(mid,y));

	}
	return 0;
}