3680: 吊打XXX

思路：
　　模拟退火。
代码：
跑的特别慢。。。
 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring> 
 4 #include<cctype>
 5 #include<cmath>
 6  
 7 using namespace std;
 8  
 9 const int N = 10010;
10 struct Node{
11     double x,y,w;
12 }d[N],ans;
13 int n;
14 double minans = 1e18;
15  
16 double dis(Node a,Node b) {
17     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
18 }
19 double check(Node p) {
20     double ret = 0;
21     for (int i=1; i<=n; ++i) 
22         ret += d[i].w*dis(p,d[i]);
23     if (ret < minans)
24         ans = p,minans = ret;
25     return ret;
26 }
27 double Rand() {
28     return rand()%1000/1000.0;
29 }
30 void SA() {
31     double T = 100000;
32     Node now = ans;
33     while (T > 0.001) {
34         Node nxt;
35         nxt.x = now.x+T*(Rand()*2.0-1.0);
36         nxt.y = now.y+T*(Rand()*2.0-1.0);
37         double Delta = check(now)-check(nxt);
38         if (Delta > 0 || exp(Delta/T)>Rand()) now = nxt;
39         T *= 0.993;
40     }
41     for (int i=1; i<=1000; ++i) {
42         Node nxt;
43         nxt.x = ans.x+T*(Rand()*2.0-1.0);
44         nxt.y = ans.y+T*(Rand()*2.0-1.0);
45         check(nxt);
46     }
47 }
48 int main() {
49     srand(19970815); 
50     scanf("%d",&n);
51     ans.x = ans.y = 0;
52     for (int i=1; i<=n; ++i) {
53         scanf("%lf%lf%lf",&d[i].x,&d[i].y,&d[i].w);
54         ans.x += d[i].x;
55         ans.y += d[i].y;
56     }
57     ans.x /= (double)n;
58     ans.y /= (double)n;
59     SA();
60     printf("%.3lf %.3lf",ans.x,ans.y); 
61     return 0;
62 }