03-树1. 二分法求多项式单根

输入样例：
3 -1 -3 1
-0.5 0.5
输出样例：
0.33

#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

double (double a3, double a2, double a1, double a0, double val)
{
    return a3 * pow(val,3.0) + a2 * pow(val,2.0) + a1 * pow(val,1.0) + a0;
}
void BinarySearch(double a, double b,double a3, double a2, double a1, double a0)
{
    double beg = a, end = b;
    double mid = .0;
    double midResult = .0, begResult = .0, endResult = .0;
    begResult = Compute(a3, a2, a1, a0, beg);
    endResult = Compute(a3, a2, a1, a0, end);
    while(begResult * endResult <= 0 )
    {
        mid = (beg + end) / 2.0;
        midResult = Compute(a3, a2, a1, a0, mid);
        if( abs(midResult) < 0.0001)
        {
            cout << setiosflags(ios::fixed) << setprecision(2) << mid << endl;
            break;
        }
        else if(midResult * begResult > 0)
        {
            beg = mid;
        }
        else
        {
            end = mid;
        }
        begResult = Compute(a3, a2, a1, a0, beg);
        endResult = Compute(a3, a2, a1, a0, end);
    }
}

int main()
{
    double a3 = 0, a2 = 0, a1 = 0, a0 = 0;
    double  a = 0, b = 0;
    cin >> a3 >> a2 >> a1 >> a0
        >> a >> b;
    BinarySearch(a, b, a3, a2, a1, a0);
    return 0;
}