[JSOI2004]平衡点

#include<iostream>
#include<cstdio>
#include<ctime>
#include<cstdlib>
#include<cmath>
#define ll long long
#define N 100005

struct P{int x,y,w;}p[N];

ll n;

 double ansx,ansy;

inline long double find(long double x,long double y){
	double ans = 0;
	for(int i = 1;i <= n;++i)
	ans += std::sqrt((x - p[i].x) * (x - p[i].x) + (y - p[i].y) * (y - p[i].y)) * p[i].w;
	return ans;
}

int main(){
	srand((int)time(NULL));
	scanf("%lld",&n);
	for(int i = 1;i <= n;++i){
		scanf("%d%d%d",&p[i].x,&p[i].y,&p[i].w);
		ansx += p[i].x;
		ansy += p[i].y;
	}
	ansx = (ansx) / (1.0 * n);
	ansy = (ansy) / (1.0 * n);
	double eps = 1e-15;
	double T = 200;//初始温度 
	while(T > eps){//终止态 
//		std::cout<<T<<" "<<(rand() * 2 - RAND_MAX) * T<<std::endl;
		double nowx = ansx + ((rand() * 2 - RAND_MAX) * T);//在值域[ansx - t,ansx + t];中挑选一个随机数
		double nowy = ansy + ((rand() * 2 - RAND_MAX) * T); //在值域[ansy - t,ansy + t];中挑选一个随机数
		long double z = find(nowx,nowy) - find(ansx,ansy);
		if(z < 0)
		ansx = nowx,ansy = nowy;
		else
		if(exp(-z / T) * RAND_MAX > rand())//随机接受 
		ansx = nowx,ansy = nowy;
		T *= 0.997;//降温速率 
	}
	printf("%.3lf %.3lf\n",ansx,ansy);
}