poj2560

 1 //Accepted    240 KB    0 ms
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cmath>
 5 const int MAXN =105;
 6 const int inf = 100000000;
 7 double x[MAXN],y[MAXN];
 8 double a[MAXN][MAXN];
 9 bool vis[MAXN];
10 double dis[MAXN];
11 int n;
12 void pre()
13 {
14     for (int i=0;i<n;i++)
15     {
16         for (int j=0;j<n;j++)
17         {
18             a[i][j]=sqrt((double )(x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
19         }
20     }
21 }
22 double prim()
23 {
24     double ans=0;
25     memset(vis,0,sizeof(vis));
26     for (int i=0;i<n;i++)
27     dis[i]=(double )inf;
28     dis[0]=0;
29     for (int i=0;i<n;i++)
30     {
31         double temp=(double )inf;
32         int k=0;
33         for (int j=0;j<n;j++)
34         {
35             if (vis[j]) continue;
36             if (temp>dis[j])
37             {
38                 temp=dis[j];
39                 k=j;
40             }
41         }
42         vis[k]=1;
43         ans+=temp;
44         for (int j=0;j<n;j++)
45         {
46             if (vis[j]) continue;
47             if (dis[j]>a[k][j])
48             {
49                 dis[j]=a[k][j];
50             }
51         }
52     }
53     return ans;
54 }
55 int main()
56 {
57     while (scanf("%d",&n)!=EOF)
58     {
59         for (int i=0;i<n;i++)
60         {
61             scanf("%lf%lf",&x[i],&y[i]);
62         }
63         pre();
64         double ans=prim();
65         printf("%.2f\n",ans);
66     }
67     return 0;
68 }