joj 1805

求外接圆圆心的一道题

#include<iostream>
#include<stdio.h>
#include<math.h>
using namespace std;
struct Point{
       double x;
       double y;
};
Point  circle_center(Point  pt[3]) 
{ 
           double  x1,x2,x3,y1,y2,y3; 
           double  x  =  0; 
           double  y  =  0; 

           x1  =  pt[0].x; 
           x2  =  pt[1].x; 
           x3  =  pt[2].x; 
           y1  =  pt[0].y; 
           y2  =  pt[1].y; 
           y3  =  pt[2].y; 

           x=((y2-y1)*(y3*y3-y1*y1+x3*x3-x1*x1)-(y3-y1)*(y2*y2-y1*y1+x2*x2-x1*x1))/(2*(x3-x1)*(y2-y1)-2*((x2-x1)*(y3-y1)));
            y=((x2-x1)*(x3*x3-x1*x1+y3*y3-y1*y1)-(x3-x1)*(x2*x2-x1*x1+y2*y2-y1*y1))/(2*(y3-y1)*(x2-x1)-2*((y2-y1)*(x3-x1)));
           Point center;
           center.x  =  x  ; 
           center.y  =  y  ; 
           return center;
}
int main()
{
    Point p[3];
    while(scanf("%lf%lf%lf%lf%lf%lf",&p[0].x,&p[0].y,&p[1].x,&p[1].y,&p[2].x,&p[2].y)!=EOF)
    {
        Point c=circle_center(p);
        double r=sqrt((p[0].x-c.x)*(p[0].x-c.x)+(p[0].y-c.y)*(p[0].y-c.y));
        printf("(x");
        if(c.x>0)
            printf(" - %.3lf",fabs(c.x));
        if(c.x<0)
            printf(" + %.3lf",fabs(c.x));
        printf(")^2 + (y");
        if(c.y>0)
            printf(" - %.3lf",fabs(c.y));
        if(c.y<0)
            printf(" + %.3lf",fabs(c.y));
        printf(")^2 = %.3lf^2\n",fabs(r));
        double p=c.x*c.x+c.y*c.y-r*r;
        double c1=2*c.x;
        double c2=2*c.y;
        printf("x^2 + y^2");
        if(c1>0)
          printf(" - %.3lfx",fabs(c1));
        if(c1<0)
          printf(" + %.3lfx",fabs(c1));
        if(c2>0)
          printf(" - %.3lfy",fabs(c2));
        if(c2<0)
          printf(" + %.3lfy",fabs(c2));
        if(p>0)
          printf(" + %.3lf",fabs(p));
        if(p<0)
          printf(" - %.3lf",fabs(p));
        printf(" = 0\n");
        printf("\n");
    }
}