pojA Star not a Tree?

题目链接

pojA Star not a Tree?

题解

啊，模拟退火是个好东西

模拟退火即可

代码

#include<cmath>
#include<cstdio>
#include<algorithm>
inline int read() {
	int x = 0,f = 1;
	char c = getchar();
	while(c < '0' || c > '9')c = getchar();
	while(c <= '9' && c >= '0') x = x * 10 + c - '0',c = getchar();
	return x * f;
}
#define INF 1e18
#define eps 1e-10
int n;
struct Node {
	double x,y;
} p[101];
double dis(Node a,Node b) {
	return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
double calc(Node a) {
	double sum = 0;
	for(int i = 1;i <= n;++ i)
		sum += dis(a,p[i]);
	return sum;
}
#define T 100
#define delta 0.98 

double Rand() {
	return (double) rand() / (double)RAND_MAX;
}
#define IT 5
double dx[7] = {1,0,-1,0,1};
double solve() {
	Node x = p[1];
	double res = calc(x);
	double t = T;
	while(t > eps) {
		for(int i = 1;i < IT; ++ i) {
			for(int i = 0;i <= 4;++ i) {
				Node nx = x;
				nx.x += dx[i] * Rand() * t;
				nx.y += dx[i + 1] * Rand() * t;
				double nxres = calc(nx);
				if(nxres < res || Rand() >= exp((nxres - res) / res)) res = nxres,x = nx;
			}
		}
		t *= delta;
	}
	return res;
}
int main() {
	srand(20010901);
	n = read();
	for(int i = 1;i <= n;++ i)
		scanf("%lf%lf",&p[i].x,&p[i].y);
	double ans = INF;
	for(int i = 1;i <= 10;++ i) {
		ans = std:: min(ans,solve());
	}
	printf("%.0lf\n",ans);
}