HDOJ 2199 Can you solve this equation?

Can you solve this equation?

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

Total Submission(s): 16602    Accepted Submission(s): 7371

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

2100-4

 

Sample Output

1.6152No solution!

求导知道函数是单调的所以直接采用二分法求解

#include<stdio.h>#include<math.h>double fn(double x){return (8*x*x*x*x + 7*x*x*x + 2*x*x + 3*x + 6); }double check(double y){double a,b,mid;a=0.0;b=100.0;mid=50.0;while(fabs(fn(mid)-y)>0.000001){if(fn(mid)-y<0){a=mid;mid=(a+b)/2;}if(fn(mid)-y>0){b=mid;mid=(a+b)/2;}}return mid;}int main(){int t;double y;scanf("%d",&t);while(t--){scanf("%lf",&y);if(fn(0)>y||fn(100)<y){printf("No solution!\n");continue;}elseprintf("%.4lf\n",check(y));}return 0;}