题解 | #[NOIP2001]一元三次方程求解#

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

double a,b,c,d;

double f(double x)
{
    return a*x*x*x+b*x*x+c*x+d;
}
double bs(double l,double r)
{
    while(r-l>1e-8)
    {
        double mid = (r+l)/2;
        if(f(mid)*f(l)<=0) r=mid;
        else l=mid;
    }
    return l;
}
int main()
{
    scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
    for(double i=-100;i<100;i++)
    {
        if(f(i)*f(i+1)>0) continue;
        if(abs(f(i+1))<1e-8)  // 防止答案右端点被下一个区间再次的使用到
        {
            printf("%.2f ",i+1);
            i++;
            continue;
        }
        double t=bs(i,i+1);
        printf("%.2f ",t);
    }
}