[BZOJ2823][BZOJ1336][BZOJ1337]最小圆覆盖(随机增量法)

算法介绍网上有很多，不解释了。

给出三点坐标求圆心方法：https://blog.csdn.net/liyuanbhu/article/details/52891868

记得先random_shuffle()一下。

 #include<cmath>
 #include<cstdio>
 #include<algorithm>
 #define rep(i,l,r) for (int i=(l); i<=(r); i++)
 using namespace std;

 const int N=;
 const double eps=1e-;
 int n;
 double r;
 struct P{ double x,y; }a[N],c;

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

 P get(P &A,P &B,P &C){
     double a=A.x-B.x,b=A.y-B.y,c=A.x-C.x,d=A.y-C.y;
     double e=((sqr(A.x)-sqr(B.x))-(sqr(B.y)-sqr(A.y)))/;
     double f=((sqr(A.x)-sqr(C.x))-(sqr(C.y)-sqr(A.y)))/;
     return (P){(d*e-b*f)/(a*d-b*c),(a*f-c*e)/(a*d-b*c)};
 }

 void work(){
     random_shuffle(a+,a+n+);
     r=; c=a[];
     rep(i,,n) if (dis(c,a[i])>r+eps){
         c=a[i]; r=;
         rep(j,,i-) if (dis(a[j],c)>r+eps){
             c=(P){(a[i].x+a[j].x)/,(a[i].y+a[j].y)/}; r=dis(c,a[i]);
             rep(k,,j-) if (dis(a[k],c)>r+eps){
                 c=get(a[i],a[j],a[k]); r=dis(c,a[i]);
             }
         }
     }
 }

 int main(){
     scanf("%d",&n);
     rep(i,,n) scanf("%lf%lf",&a[i].x,&a[i].y);
     work(); printf("%lf\n%lf %lf\n",r,c.x,c.y);
     return ;
 }