[日常摸鱼]poj2420 A Star not a Tree?

题意：给定$n$个点，找一个点使得这个点到所有点的距离之和最小，求出这个最小距离

 

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传说中的模拟退火…

#include<cstdio>
#include<ctime>
#include<cmath>
#include<cstdlib> 
const int N=105;
struct point
{
    double x,y;
}ps[N];
int n;
double t,ans,tans,tx,ty,nx,ny,temp;

inline double get(int x){return 1.0*((rand()%x)*(rand()%x)%x);}
inline double sqr(double x){return x*x;}
inline double dis(double x,double y,point &p)
{
    return sqrt(sqr(x-p.x)+sqr(y-p.y));
}
inline double calc(double x,double y)
{
    double res=0;
    for(register int i=1;i<=n;i++)res+=dis(x,y,ps[i]);
    return res;
}
int main()
{
    scanf("%d",&n);nx=ny=0;t=100000;
    for(register int i=1;i<=n;i++)
    {
        scanf("%lf%lf",&ps[i].x,&ps[i].y);
        nx+=ps[i].x;ny+=ps[i].y;
    }
    nx/=n;ny/=n;tans=ans=calc(nx,ny);
    while(t>0.02)
    {
        tx=ty=0;
        for(register int i=1;i<=n;i++)
        {
            tx+=(ps[i].x-nx)/dis(nx,ny,ps[i]);
            ty+=(ps[i].y-ny)/dis(nx,ny,ps[i]);
        }
        temp=calc(nx+tx*t,ny+ty*t);
        if(temp<ans)
        {
            tans=ans=temp;nx+=tx*t;ny+=ty*t;
        }else if(log((temp-ans)/t)<get(10000)/10000.0)
        {
            ans=temp;nx+=tx*t;ny+=ty*t;
        }
        t*=0.9;
    }
    if(tans<ans)ans=tans;
    printf("%.0lf",ans);
    return 0;
}

 

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