(DS1.5.6)POJ 2242 The Circumference of the Circle(一直三个点的坐标,求外接圆的周长)

/* * POJ_2242.cpp * *  Created on: 2013年10月23日 *      Author: Administrator */#include <iostream>#include <cstdio>#include <cmath>using namespace std;int main(){double x1,y1,x2,y2,x3,y3;const double PI = 3.141592653589793;while(scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3)!=EOF){double a = sqrt(abs(x2-x1)*abs(x2-x1) + abs(y2-y1)*abs(y2-y1));double b = sqrt(abs(x2-x3)*abs(x2-x3) + abs(y2-y3)*abs(y2-y3));double c = sqrt(abs(x3-x1)*abs(x3-x1) + abs(y3-y1)*abs(y3-y1));double p = (a+b+c)/2;double s = sqrt(p*(p-a)*(p-b)*(p-c));double d = a*b*c/(2*s);//外接圆的直径        double l = d*PI;        printf("%.2lf\n",l);}return 0;}