【BZOJ2823】[AHOI2012]信号塔（最小圆覆盖）

【BZOJ2823】[AHOI2012]信号塔（最小圆覆盖）

题面

BZOJ

洛谷

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BZOJ1

BZOJ2

洛谷

题解

模板题。。。

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
#define MAX 1000100
const double eps=1e-10;
const double Pi=acos(-1);
struct Point{double x,y,ang;};
bool operator<(Point a,Point b){return (a.ang!=b.ang)?a.ang<b.ang:a.x<b.x;}
Point operator+(Point a,Point b){return (Point){a.x+b.x,a.y+b.y};}
Point operator-(Point a,Point b){return (Point){a.x-b.x,a.y-b.y};}
Point operator*(Point a,double b){return (Point){a.x*b,a.y*b};}
Point operator/(Point a,double b){return (Point){a.x/b,a.y/b};}
double operator*(Point a,Point b){return a.x*b.x+a.y*b.y;}
double Cross(Point a,Point b){return a.x*b.y-a.y*b.x;}
double Len(Point a){return sqrt(a.x*a.x+a.y*a.y);}
double Dis(Point a,Point b){return Len(a-b);}
Point Rotate(Point p,double a){double c=cos(a),s=sin(a);return (Point){p.x*c-p.y*s,p.x*s+p.y*c};}
struct Line{Point a,v;};
Point Intersection(Line a,Line b)
{
	Point c=b.a-a.a;
	double t=Cross(b.v,c)/Cross(b.v,a.v);
	return a.a+a.v*t;
}
Line GetHalfLine(Line a)
{
	Point b=a.a+a.v*0.5;
	return (Line){b,Rotate(a.v,Pi/2)};
}
struct Circle{Point o;double r;}O;
void GetCircle(Point *p,int n)
{
	random_shuffle(&p[1],&p[n+1]);
	for(int i=1;i<=n;++i)
		if(Dis(O.o,p[i])>O.r)
		{
			O.o=p[i];O.r=0;
			for(int j=1;j<i;++j)
				if(Dis(O.o,p[j])>O.r)
				{
					O.o=(p[i]+p[j])*0.5;O.r=Dis(p[i],p[j])*0.5;
					for(int k=1;k<j;++k)
						if(Dis(O.o,p[k])>O.r)
						{
							O.o=Intersection(GetHalfLine((Line){p[i],p[j]-p[i]}),GetHalfLine((Line){p[i],p[k]-p[i]}));
							O.r=Dis(O.o,p[i]);
						}
				}
		}
	printf("%.2lf %.2lf %.2lf\n",O.o.x,O.o.y,O.r);
}
int n;Point p[MAX];
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;++i)scanf("%lf%lf",&p[i].x,&p[i].y);
	GetCircle(p,n);
	return 0;
}