2018ICPC南京D. Country Meow

题目：

题意：三维里有n个点，找一个最小的球将所有点覆盖。

题解：退火法模拟的一道板子题。

#include <stdio.h>
#include <iostream>
#include <math.h>
using namespace std;
const int MAXN=105;
const double EPS=1e-8;
struct Point{
    double x,y,z;
    Point(double _x=0,double _y=0,double _z=0){
        x=_x;y=_y;z=_z;
    }
};
Point Dots[MAXN];
int n;
 
double Distance(Point a,Point b){
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z));
}
double Solve(){
    double Step=100000,ans=1e9,mt;
    Point z=Point(0.0,0.0,0.0);
    int s=0;
    while(Step>EPS){
        for(int i=1;i<=n;++i){
            if(Distance(z,Dots[s])<Distance(z,Dots[i])){
                s=i;
            }
        }
        mt=Distance(z,Dots[s]);
        ans=min(ans,mt);
        z.x+=(Dots[s].x-z.x)/mt*Step;
        z.y+=(Dots[s].y-z.y)/mt*Step;
        z.z+=(Dots[s].z-z.z)/mt*Step;
        Step*=0.98;
    }return ans;
}
int main(){

        scanf("%d",&n);
        
        for(int i=1;i<=n;++i){
            double x,y,z;scanf("%lf%lf%lf",&x,&y,&z);
            Dots[i]=Point(x,y,z);
        }
        printf("%.15f",Solve());
    
}

 这题一开始没仔细看题只看了输出就被吓到了（还没学到立体几何）以为很难，后面没题可做了队友hcc发现就是一个最小球覆盖问题，然后我回忆起来前几天看到了这个板子就这套了一下就A了。