二分法HDU2199

Can you solve this equation?

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1466    Accepted Submission(s): 737

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


这道题在精度方面要求较好，今年的亚洲赛也有一道是精度问题的。
#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
double f(double x){
  return 8*pow(x,4.0)+7*pow(x,3.0)+2*pow(x,2.0)+3*x+6;
}
double y;
int main(){
  int n;
  double r,l;
  cin>>n;
  for(int i = 1;i <= n;i ++){
    cin>>y;
    r = 0;
    l = 100;
    if(f(0) <= y && y <= f(100)){
    while(l - r > 1e-7){
      double len = (l + r)/2;
      if(f(len) > y){
        l = len - 1e-7;
      }
        else r = len + 1e-7;
    }
    printf("%.4lf\n",(l + r)/2);
  }
    else printf("No solution!\n");
  }
}

   
   
   
   

    
    
    
    2 100 -4
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    1.6152 No solution!