hdoj 2199 Can you solve this equation?【浮点型数据二分】

Can you solve this equation?

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 12766    Accepted Submission(s):
5696

Problem Description

Now,given the equation 8*x^4 + 7*x^3 + 2*x^2 + 3*x + 6
== Y,can you find its solution between 0 and 100;
Now please try your
lucky.

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 a real number Y (fabs(Y) <= 1e10);

Output

For each test case, you should just output one real
number(accurate up to 4 decimal places),which is the solution of the equation,or
“No solution!”,if there is no solution for the equation between 0 and 100.

Sample Input

2

100

-4

Sample Output

1.6152

No solution!

#include<stdio.h>
#include<string.h>
double f(double v)//用来计算方程结果（即y的值）
{
	return 8*v*v*v*v+7*v*v*v+2*v*v+3*v+6;
}
int main()
{
	int t;
	double y,l,r,mid;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%lf",&y);
		if(y<f(0)||y>f(100))
		{
			printf("No solution!\n");
			continue;
		}
		l=0;r=100;mid=0;
		while((r-l) > 1e-10)//题目要求精度为小数点后四位，最好把精度调高
		{
			mid=(l+r)/2;//每次折半取x的范围
			if(f(mid) < y)
			    l=mid;
			else
			    r=mid;
		}
		printf("%.4lf\n",mid);
	}
}