HDU 2199 --Can you solve this equation?【二分水問題】

Can you solve this equation?
Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others) Total Submission(s): 13018    Accepted Submission(s): 5835
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 <cstdio>
#include <cmath>

double change(double x){
	 return 8 * pow(x, 4) + 7 * pow(x, 3) + 2 * pow(x, 2) + 3 * x + 6; 
}

int main (){
	int  T;
	scanf("%d", &T);
	while(T--){
		double sum;
		scanf("%lf", &sum);
		double l = 0, r = 100;
		if(sum < change(0) || sum > change(100.0)){
			printf("No solution!
");
			continue;
		}
		else{
			while(r - l > 1e-6){
				double mid = (l + r) / 2;
				if(change(mid) > sum)
					r = mid;
				else 
					l = mid;
			}
			printf("%.4lf
", r);
		}
	}
	return 0;
}