HDU 2199 Can you solve this equation?（二分解方程）

传送门：

http://acm.hdu.edu.cn/showproblem.php?pid=2199

Can you solve this equation?

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 25039    Accepted Submission(s): 10776

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!

 

 

Author

Redow

 

 

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代码：

#include<iostream>
#include<algorithm>
#include<stdio.h>
#include<queue>
#include<set>
#include<map>
#include<string>
#include<memory.h>
#include<math.h>
#define eps 1e-7
using namespace std;
int y;
double f(double x)
{
    return 8*pow(x,4)+7*pow(x,3)+2*pow(x,2)+3*x+6-y;
}
double ff()
{
    double l=0,h=100;
    double mid;
    while(h-l>=eps)//精度控制
    {
        mid=(l+h)/2;
        if(f(mid)>0)
        {
            h=mid;
        }else
        {
            l=mid;
        }
    }
    return mid;
}
int main()
{
    int t;
    cin>>t;
    while(t--)
    {
        cin>>y;
        if(f(0)*f(100)>0)//与x轴无交点了
            cout<<"No solution!"<<endl;
        else
            printf("%0.4lf\n",ff());
    }
    return 0;
}