ZOJ1090 The Circumference of the Circle

计算几何题，使用的数学公式参考http://topic.youkuaiyun.com/t/20050329/22/3892541.html

<!--<br /> <br /> Code highlighting produced by Actipro CodeHighlighter (freeware)<br /> http://www.CodeHighlighter.com/<br /> <br /> --> #include < iostream >
#include < iomanip >
#include < cmath >
using namespace std;

const double PI = 3.141592653589793 ;
double Distance( double x1, double y1, double x2, double y2)
{ // 两点间的距离
double deltaX = x1 - x2;
double deltaY = y1 - y2;
return sqrt(deltaX * deltaX + deltaY * deltaY);
}
double CaculateCircum( double x1, double y1, double x2, double y2, double x3, double y3)
{ // 计算三角形外接圆周长
// 海伦公式计算三角形面积
double a,b,c,L,S;
a = Distance(x1,y1,x2,y2);
b = Distance(x2,y2,x3,y3);
c = Distance(x1,y1,x3,y3);
L = (a + b + c) / 2 ;
S = sqrt(L * (L - a) * (L - b) * (L - c));
// 计算三角形外接圆周长
return PI * a * b * c / ( 2 * S);
}
int main( void )
{
double x1,y1,x2,y2,x3,y3,circum;
while (cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3)
{
circum = CaculateCircum(x1,y1,x2,y2,x3,y3);
cout << fixed << setprecision( 2 ) << circum << endl;
}
return 0 ;
}