HDU4720+三角形外接圆

/*
几何
求给定三角形的外接圆圆心 
方法：求解二元方程组 
*/
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdlib.h>
const double pi = acos(-1.0);
const double eps = 1e-8;
struct Point{
    double x,y;
};
struct Circle{
    Point center;
    double r;
};
Point a,b,c,tp;
Circle cc;

double dis( Point a,Point b ){
    return sqrt( (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y) );
}

bool JudgeTriangle( Point a,Point b,Point c ){
    double len1 = dis( a,b );
    len1 *= len1;
    double len2 = dis( a,c );
    len2 *= len2;
    double len3 = dis( b,c );
    len3 *= len3;
    if( len1+len2-len3<=0||len1+len3-len2<=0||len2+len3-len1<=0 ) return false;
    else return true;
}/*判断是否是钝角三角形*/

void GetCircle( Point a,Point b,Point c ){
    bool judge = JudgeTriangle( a,b,c );
    if( judge==false ){
        double ans;
        int op ;
        double len1 = dis( a,b );
        ans = len1;
        op = 1;
        double len2 = dis( a,c );
        if( len2>ans ){
            ans = len2;
            op = 2;
        }
        double len3 = dis( b,c );
        if( len3>ans ){
            ans = len3;
            op = 3;
        }
        cc.r = ans / 2.0;
        if( op==1 ){
            cc.center.x = ( a.x+b.x )/2.0;
            cc.center.y = ( a.y+b.y )/2.0;
        }
        else if( op==2 ){
            cc.center.x = ( a.x+c.x )/2.0;
            cc.center.y = ( a.y+c.y )/2.0;
        }
        else {
            cc.center.x = ( b.x+c.x )/2.0;
            cc.center.y = ( b.y+c.y )/2.0;
        }
        return ;
    }/*钝角三角形*/
    double x1 = a.x,x2 = b.x,x3 = c.x;
    double y1 = a.y,y2 = b.y,y3 = c.y;
    cc.center.x=((y2-y1)*(y3*y3-y1*y1+x3*x3-x1*x1)-(y3-y1)*(y2*y2-y1*y1+x2*x2-x1*x1))/(2*(x3-x1)*(y2-y1)-2*((x2-x1)*(y3-y1)));    
    cc.center.y=((x2-x1)*(x3*x3-x1*x1+y3*y3-y1*y1)-(x3-x1)*(x2*x2-x1*x1+y2*y2-y1*y1))/(2*(y3-y1)*(x2-x1)-2*((y2-y1)*(x3-x1)));   
    cc.r = dis( cc.center,a );
    return ;    
}/*求外接圆圆心*/ 

int main(){
    int T;
    scanf("%d",&T);
    int ca = 1;
    while( T-- ){
        scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&a.x,&a.y,&b.x,&b.y,&c.x,&c.y,&tp.x,&tp.y);
        GetCircle( a,b,c );
        printf("Case #%d: ",ca++);
        if( dis( tp,cc.center )<=cc.r ) printf("Danger
");
        else printf("Safe
");
    }
    return 0;
}