UVA 438 (The Circumference of the Circle) Solution

Hints:
Suppose that the coordinates of the three points are  (a1,a2),$(a_1,a_2),$ (b1,b2),$(b_1,b_2),$ and (c1,c2).$(c_1,c_2).$

Compute the following three values.  If the value of  d is 0, they lie on a line so there's no circle to have a center.

            d=(a1−b1)(b2−c2)−(b1−c1)(a2−b2)

                           u=a21−b21+a22−b222

                           v=b21−c21+b22−c222

Then the center has coordinates  (x,y)$(x,y)$  where

                      x=u(b2−c2)−v(a2−b2)d

                      y=v(a1−b1)−u(b1−c1)d

Solve in C:


#include<stdio.h>
#include<math.h>
int main(){

double a1,a2,b1,b2,c1,c2,x,y,pi=3.141592653589793,d,u,v,r,c;
while(scanf("%lf%lf%lf%lf%lf%lf",&a1,&a2,&b1,&b2,&c1,&c2)!=EOF)
{
    d=(a1-b1)*(b2-c2)-(b1-c1)*(a2-b2);
  u=(((a1*a1)-(b1*b1))+((a2*a2)-(b2*b2)))/2.0;
  v=((b1*b1)-(c1*c1)+(b2*b2)-(c2*c2))/2.0;

  x=((u*(b2-c2))-(v*(a2-b2)))/d;

 y=((v*(a1-b1))-(u*(b1-c1)))/d;

    r=sqrt(((x-a1)*(x-a1)+(y-a2)*(y-a2)));
    c=2*pi*r;

    printf("%.2lf\n",c);
}


}

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