外接圆周长.cpp

acm 常用算法和代码库

#include <iostream>
#include <cmath>

using namespace std;
#define PI 3.141592653589793
int main()
{
    double a,b,c;
	double x1,x2,x3,y1,y2,y3;
	double sinA,cosA,r;
	while(cin>>x1>>y1>>x2>>y2>>x3>>y3)
	{
		a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        b=sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
		c=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
		cosA=(b*b+c*c-a*a)/(2*b*c);
		sinA=sqrt(1-cosA*cosA);
		r=a/sinA;
		printf("%.2f\n",PI*r);
	}
	return 0;
}