【题解】poj2420 A Star not a Tree? 模拟退火

题目链接

写个srand((unsigned)time(0))还RE了，怒写一发八位质数AC（逃

#include<cstdio>
#include<cmath>
#include<ctime>
#include<cstdlib>
int n;
double ansx,ansy,ans;
struct node{
	double x,y;
}p[110];
double dis(double x,double y,node a)
{
	return sqrt((x-a.x)*(x-a.x)+(y-a.y)*(y-a.y));
}
double getans(double x,double y)
{
	double ret=0.0;
	for(int i=1;i<=n;i++)
	    ret+=dis(x,y,p[i]);
	return ret;
}
void SA()
{
	double t=1e5;
	while(t>1e-5)
	{
		double nx=0,ny=0;
		for(int i=1;i<=n;i++)
		    nx+=(p[i].x-ansx)/dis(ansx,ansy,p[i]),ny+=(p[i].y-ansy)/dis(ansx,ansy,p[i]);
		double now=getans(ansx+nx*t,ansy+ny*t);
		if(now<ans)
		    ans=now,ansx+=nx*t,ansy+=nx*t;
		else if(exp((ans-now)/t)*RAND_MAX>rand())ansx+=nx*t,ansy+=ny*t,ans=now;
		t*=0.957;
	}
}
int main()
{
	//freopen("in.txt","r",stdin);
	srand(19260817);
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
        scanf("%lf%lf",&p[i].x,&p[i].y),ansx+=p[i].x,ansy+=p[i].y;
    ansx/=n;ansy/=n;ans=getans(ansx,ansy);
    SA();
    printf("%.0f\n",ans);
    return 0;
}

总结

依旧模拟退火练手