试题 算法训练 一元三次方程求解

#include <stdlib.h>
#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <string.h>
#include <math.h>
using namespace std;
double a,b,c,d;
double ans[5];
int k=0;
double f(double x)
{
	return a*x*x*x+b*x*x+c*x+d;
}
int main()
{	
	cin>>a>>b>>c>>d;
	double i;
	int cnt=0;//找到的实根个数 
	for(i=-100;i<=100;i++)
	{
		double left=i,right=i+1;
		if(f(left)*f(right)==0)//left和right肯定有一个是根 
		{
			if(f(left)==0)
			ans[k++]=left;
		}
		else if(f(left)*f(right)<0)//某一个根肯定在left和right之间 
		{
			while((fabs(right-left))>=0.00001)
			{
				double mid=(left+right)/2.0;
				if(f(left)*f(mid)<=0)
				right=mid;
				else
				left=mid;
			}
			//printf("%.2lf\n",left);
			ans[k++]=left;
		} 
		else//根不在 left和right之间 
		 	continue;
	}
	for(int j=0;j<k;j++)
	{
		if(i==k-1)
		printf("%.2lf\n",ans[j]);
		else
		printf("%.2lf ",ans[j]);
	}
	return 0;
}