HDU-4720 Naive and Silly Muggles 圆的外心

　　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。。

  1 //STATUS:C++_AC_0MS_292KB

  2 #include <functional>

  3 #include <algorithm>

  4 #include <iostream>

  5 //#include <ext/rope>

  6 #include <fstream>

  7 #include <sstream>

  8 #include <iomanip>

  9 #include <numeric>

 10 #include <cstring>

 11 #include <cassert>

 12 #include <cstdio>

 13 #include <string>

 14 #include <vector>

 15 #include <bitset>

 16 #include <queue>

 17 #include <stack>

 18 #include <cmath>

 19 #include <ctime>

 20 #include <list>

 21 #include <set>

 22 #include <map>

 23 using namespace std;

 24 //#pragma comment(linker,"/STACK:102400000,102400000")

 25 //using namespace __gnu_cxx;

 26 //define

 27 #define pii pair<int,int>

 28 #define mem(a,b) memset(a,b,sizeof(a))

 29 #define lson l,mid,rt<<1

 30 #define rson mid+1,r,rt<<1|1

 31 #define PI acos(-1.0)

 32 //typedef

 33 typedef __int64 LL;

 34 typedef unsigned __int64 ULL;

 35 //const

 36 const int N=25;

 37 const int INF=0x3f3f3f3f;

 38 const int MOD=1000000007,STA=8000010;

 39 const LL LNF=1LL<<60;

 40 const double EPS=1e-8;

 41 const double OO=1e60;

 42 const int dx[4]={-1,0,1,0};

 43 const int dy[4]={0,1,0,-1};

 44 const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};

 45 //Daily Use ...

 46 inline int sign(double x){return (x>EPS)-(x<-EPS);}

 47 template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}

 48 template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}

 49 template<class T> inline T lcm(T a,T b,T d){return a/d*b;}

 50 template<class T> inline T Min(T a,T b){return a<b?a:b;}

 51 template<class T> inline T Max(T a,T b){return a>b?a:b;}

 52 template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}

 53 template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}

 54 template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}

 55 template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}

 56 //End

 57 

 58 int T;

 59 

 60 struct Point{

 61     double x,y;

 62 }p[5];

 63 

 64 double dist(Point a,Point b)

 65 {

 66     return sqrt( (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y) );

 67 }

 68 

 69 double sqr(double x){ return x * x; }

 70 

 71 void Ci(Point p0 , Point p1 , Point p2 , Point &cp)

 72 {

 73     double a1=p1.x-p0.x,b1 = p1.y - p0.y,c1 = (sqr(a1) + sqr(b1)) / 2;

 74     double a2=p2.x-p0.x,b2 = p2.y - p0.y,c2 = (sqr(a2) + sqr(b2)) / 2;

 75     double d = a1 * b2 - a2 * b1;

 76     cp.x = p0.x + (c1 * b2 - c2 * b1) / d;

 77     cp.y = p0.y + (a1 * c2 - a2 * c1) / d;

 78 }

 79 

 80 int judge1(int& ok)

 81 {

 82     int i,j,k;

 83     double d,r,lowr;

 84     Point c,t;

 85     lowr=OO;

 86     for(i=0;i<3;i++){

 87         for(j=0;j<3;j++){

 88             if(i==j)continue;

 89             r=dist(p[i],p[j])/2;

 90             t.x=(p[i].x+p[j].x)/2;

 91             t.y=(p[i].y+p[j].y)/2;

 92             for(k=0;k==i || k==j;k++);

 93             if(dist(t,p[k])<=r){

 94                 lowr=r;

 95                 c.x=t.x,c.y=t.y;

 96             }

 97         }

 98     }

 99     if(lowr==OO)return 0;

100     if(dist(p[3],c)<=lowr)ok=1;

101     return 1;

102 }

103 

104 int main(){

105  //   freopen("in.txt","r",stdin);

106     int i,j,ca=1,ok;

107     double r,d;

108     Point c;

109     scanf("%d",&T);

110     while(T--)

111     {

112         for(i=0;i<4;i++){

113             scanf("%lf%lf",&p[i].x,&p[i].y);

114         }

115         ok=0;

116         if(judge1(ok));

117         else {

118             Ci(p[0],p[1],p[2],c);

119             r=(c.x-p[0].x)*(c.x-p[0].x)+(c.y-p[0].y)*(c.y-p[0].y);

120             d=(c.x-p[3].x)*(c.x-p[3].x)+(c.y-p[3].y)*(c.y-p[3].y);

121             if(d<=r)ok=1;

122         }

123 

124         printf("Case #%d: %s\n",ca++,ok?"Danger":"Safe");

125     }

126     return 0;

127 }