POJ 2560

 1 #include<iostream>
 2 #include<algorithm>
 3 #include<cmath>
 4 #include<iomanip>
 5 #define MAXN 105
 6 #define inf 1000000000
 7 using namespace std;
 8 
 9 typedef double elem_t;
10 
11 double point[MAXN][2];
12 double _m[MAXN][MAXN];
13 int pre[MAXN];
14 elem_t prim(int n,elem_t mat[][MAXN],int* pre);
15 int main()
16 {
17     //freopen("acm.acm","r",stdin);
18     int num;
19     int i;
20     int j;
21     double x;
22     double y;
23     cin>>num;
24     for(i = 0; i < num; ++ i)
25     {
26         cin>>point[i][0]>>point[i][1];    
27     }
28     for(i = 0; i < num; ++ i)
29     {
30         for(j = i+1; j < num; ++ j)
31         {
32             _m[i][j] = sqrt((point[i][0] - point[j][0])*(point[i][0] - point[j][0]) + (point[i][1] - point[j][1])*(point[i][1] - point[j][1]));
33             _m[j][i] = _m[i][j];
34         }
35     }
36     cout<<setiosflags(ios::fixed)<<setprecision(2)<<prim(num,_m,pre)<<endl;
37 }
38 
39 
40 elem_t prim(int n,elem_t mat[][MAXN],int* pre){
41     elem_t min[MAXN],ret=0;
42     int v[MAXN],i,j,k;
43     for (i=0;i<n;i++)
44         min[i]=inf,v[i]=0,pre[i]=-1;
45     for (min[j=0]=0;j<n;j++){
46         for (k=-1,i=0;i<n;i++)
47             if (!v[i]&&(k==-1||min[i]<min[k]))
48                 k=i;
49         for (v[k]=1,ret+=min[k],i=0;i<n;i++)
50             if (!v[i]&&mat[k][i]<min[i])
51                 min[i]=mat[pre[i]=k][i];
52     }
53     return ret;
54 }