二分法查找基础

杭电2199Can you solve this equation?

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!

这题是二分法查找。直接套模板

#include<stdio.h>
#include<math.h>
double f(double x)
{
    return  8*pow(x,4.0)+7*pow(x,3.0)+2*pow(x,2.0)+3*x+6;
}
int main()
{
    int n;
    double m, l, ll, ans, mm;
    scanf("%d",&n);
    while(n--){
        scanf("%lf",&m);
        l = 0; ll = 100;
        if(m >= f(0) && m <= f(100)){//外界条件 ； 
            while(ll-l > 1e-9){//精确度 ； 
                mm = (ll + l)/2;
                double ans = f(mm);
                if(ans > m){//二分法； 
                    ll = mm-1e-9;
                }
                else{
                    l = mm+1e-9;
                }
            }
            printf("%.4lf\n",(ll+l)/2);
        }
        else    printf("No solution!\n");
    }

    return 0 ;
}