2242.txt

北大ACM题目例程 详细的解答过程 程序实现 算法分析

#include < stdio.h>
#include <math.h>

#define dis(a,b) sqrt((x[a]-x[b])*(x[a]-x[b])+(y[a]-y[b])*(y[a]-y[b]))

int main()
{
	double x[4],y[4], r;

	while( scanf( "%lf%lf%lf%lf%lf%lf", &x[1], &y[1], &x[2], &y[2], &x[3], &y[3] ) != EOF )
	{
		r = dis(1,2) * dis(2,3) * dis(1,3) / ( 2 * fabs( (x[2]-x[1])*(y[3]-y[1]) - ( y[2]-y[1])*(x[3]-x[1]) ) );
		printf( "%.2lf\n", r * 2 * 3.1415926535898 );
	}
	return 0;
}