题目大意：求最小圆覆盖
我又写了一遍233
尼玛上一遍居然忘记random_shuffle了= =
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <algorithm>
#define M 100100
#define EPS 1e-7
using namespace std;
struct Point{
double x,y;
Point() {}
Point(double _,double __):
x(_),y(__) {}
friend istream& operator >> (istream &_,Point &p)
{
scanf("%lf%lf",&p.x,&p.y);
return _;
}
friend Point operator + (const Point &p1,const Point &p2)
{
return Point(p1.x+p2.x,p1.y+p2.y);
}
friend Point operator - (const Point &p1,const Point &p2)
{
return Point(p1.x-p2.x,p1.y-p2.y);
}
friend double operator * (const Point &p1,const Point &p2)
{
return p1.x*p2.y-p1.y*p2.x;
}
friend Point operator * (const Point &p1,double rate)
{
return Point(p1.x*rate,p1.y*rate);
}
friend double Distance(const Point &p1,const Point &p2)
{
return sqrt( (p1.x-p2.x)*(p1.x-p2.x) + (p1.y-p2.y)*(p1.y-p2.y) ) ;
}
friend Point Rotate(const Point &p)
{
return Point(-p.y,p.x);
}
}points[M];
struct Line{
Point p,v;
Line() {}
Line(const Point &_,const Point &__):
p(_),v(__) {}
friend Point Get_Intersection(const Line &l1,const Line &l2)
{
Point u=l1.p-l2.p;
double temp=(l2.v*u)/(l1.v*l2.v);
return l1.p+l1.v*temp;
}
};
struct Circle{
Point o;
double r;
Circle() {}
Circle(const Point &_,double __):
o(_),r(__) {}
bool In_Circle(const Point &p)
{
return Distance(p,o) < r + EPS ;
}
}ans;
int n;
int main()
{
int i,j,k;
srand(19980402);
cin>>n;
for(i=1;i<=n;i++)
cin>>points[i];
random_shuffle(points+1,points+n+1);
for(i=1;i<=n;i++)
{
if(!ans.In_Circle(points[i]))
{
ans=Circle(points[i],0);
for(j=1;j<i;j++)
if(!ans.In_Circle(points[j]))
{
ans=Circle((points[i]+points[j])*0.5,Distance(points[i],points[j])*0.5);
for(k=1;k<j;k++)
if(!ans.In_Circle(points[k]))
{
Line l1=Line((points[i]+points[j])*0.5,Rotate(points[i]-points[j]));
Line l2=Line((points[i]+points[k])*0.5,Rotate(points[i]-points[k]));
Point O=Get_Intersection(l1,l2);
ans=Circle(O,Distance(points[i],O));
}
}
}
}
cout<<fixed<<setprecision(3)<<ans.r<<endl;
return 0;
}
