题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4720
先两两点之间枚举，如果不能找的最小的圆，那么求外心即可。。
//STATUS:C++_AC_0MS_292KB
#include <functional>
#include <algorithm>
#include <iostream>
//#include <ext/rope>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cstring>
#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bitset>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <list>
#include <set>
#include <map>
using namespace std;
//#pragma comment(linker,"/STACK:102400000,102400000")
//using namespace __gnu_cxx;
//define
#define pii pair<int,int>
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define PI acos(-1.0)
//typedef
typedef __int64 LL;
typedef unsigned __int64 ULL;
//const
const int N=;
const int INF=0x3f3f3f3f;
const int MOD=,STA=;
const LL LNF=1LL<<;
const double EPS=1e-;
const double OO=1e60;
const int dx[]={-,,,};
const int dy[]={,,,-};
const int day[]={,,,,,,,,,,,,};
//Daily Use ...
inline int sign(double x){return (x>EPS)-(x<-EPS);}
template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
template<class T> inline T Min(T a,T b){return a<b?a:b;}
template<class T> inline T Max(T a,T b){return a>b?a:b;}
template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
//End int T; struct Point{
double x,y;
}p[]; double dist(Point a,Point b)
{
return sqrt( (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y) );
} double sqr(double x){ return x * x; } void Ci(Point p0 , Point p1 , Point p2 , Point &cp)
{
double a1=p1.x-p0.x,b1 = p1.y - p0.y,c1 = (sqr(a1) + sqr(b1)) / ;
double a2=p2.x-p0.x,b2 = p2.y - p0.y,c2 = (sqr(a2) + sqr(b2)) / ;
double d = a1 * b2 - a2 * b1;
cp.x = p0.x + (c1 * b2 - c2 * b1) / d;
cp.y = p0.y + (a1 * c2 - a2 * c1) / d;
} int judge1(int& ok)
{
int i,j,k;
double d,r,lowr;
Point c,t;
lowr=OO;
for(i=;i<;i++){
for(j=;j<;j++){
if(i==j)continue;
r=dist(p[i],p[j])/;
t.x=(p[i].x+p[j].x)/;
t.y=(p[i].y+p[j].y)/;
for(k=;k==i || k==j;k++);
if(dist(t,p[k])<=r){
lowr=r;
c.x=t.x,c.y=t.y;
}
}
}
if(lowr==OO)return ;
if(dist(p[],c)<=lowr)ok=;
return ;
} int main(){
// freopen("in.txt","r",stdin);
int i,j,ca=,ok;
double r,d;
Point c;
scanf("%d",&T);
while(T--)
{
for(i=;i<;i++){
scanf("%lf%lf",&p[i].x,&p[i].y);
}
ok=;
if(judge1(ok));
else {
Ci(p[],p[],p[],c);
r=(c.x-p[].x)*(c.x-p[].x)+(c.y-p[].y)*(c.y-p[].y);
d=(c.x-p[].x)*(c.x-p[].x)+(c.y-p[].y)*(c.y-p[].y);
if(d<=r)ok=;
} printf("Case #%d: %s\n",ca++,ok?"Danger":"Safe");
}
return ;
}