算法训练——一元三次方程求解

Posted 2020-11-25 hqx-curiosity

 

//一元三次方程求解
//直接枚举 
#include<stdio.h>
#include<math.h>
double a,b,c,d,x;
double f(double x){
	return a*x*x*x + b*x*x + c*x + d; 
} 
int main(){
	scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
	for(x=-100;x<=100;++x){
		double z = x,y = z+1;
		if(f(z) == 0){
			printf("%.2f ",z);
		}
		else{
			if((f(z) * f(y)) < 0){	//x位于z与y之间	分治 
				while(y-z >= 0.001){
					double mid = (z+y)/2;
					if((f(z) * f(mid)) <= 0){
						y = mid;
					}
					else{
						z = mid;
					}
				}
				printf("%.2f ",z);
			} 
		} 
	}
	printf("
");	 
	return 0;
}