hdu2199 Can you solve this equation? (二分+double精度)

Can you solve this equation?

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

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Total Submission(s): 14274    Accepted Submission(s): 6359

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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解析：注意精度，我这里去的时候1e-6。

代码：

#include<cstdio>
#include<cmath>
using namespace std;

double precision=1e-6; 
double y;

double f(double x)
{
  return 8*pow(x,4.0)+7*pow(x,3.0)+2*pow(x,2.0)+3*x;
}

int main()
{
  //freopen("1.in","r",stdin);
  
  int t; double l,r,mid;  
  scanf("%d",&t);
  while(t--)
    {
      scanf("%lf",&y),y-=6;
    if(y<0||y>807020300)
      {
        printf("No solution!\n");
        continue;
    }

    l=0,r=100;
    while(r-l>=precision)
      {
        mid=(l+r)/2;
        if(f(mid)<=y)l=mid;
        else r=mid;
    }
    printf("%.4lf\n",(l+r)/2);
  }
  return 0;
}