1374.cpp

杭电 acm部分代码 有兴趣的可以下载 谢谢

#include<cmath>
#include<cstdio>
void main()
{
    double x1,y1,x2,y2,x3,y3;
    while(scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3)==6){
        double a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        double b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
        double c=sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
        double s=(a+b+c)/2;
        double sq=sqrt(s*(s-a)*(s-b)*(s-c));
        double re=a*b*c/4/sq;
        printf("%.2lf\n",re*2*3.141592653589793);
    }
}
//⑴s=(a+b+c)/2
//⑵面积=(s(s-a)(s-b)(s-c))开平方根
//⑶外接圆半径=abc/(4×面积)