POJ2560 Freckles

 1 /*by SilverN*/
 2 #include<algorithm>
 3 #include<iostream>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<cmath>
 7 using namespace std;
 8 int read(){
 9     int x=0,f=1;char ch=getchar();
10     while(ch<‘0‘ || ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
11     while(ch>=‘0‘ && ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
12     return x*f;
13 }
14 const int mxn=120;
15 int n;
16 struct point{
17     double x;double y;
18 }p[mxn];
19 double dist(point a,point b){
20     return sqrt( (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y) );
21 }
22 struct edge{
23     int x,y;
24     double dis;
25 }e[mxn*mxn];int cnt=0;
26 int cmp(edge a,edge b){
27     return a.dis<b.dis;
28 }
29 int fa[mxn];
30 void init(){
31     for(int i=1;i<=n;i++)fa[i]=i;
32 }
33 int find(int x){
34     if(fa[x]==x)return x;
35     return fa[x]=find(fa[x]);
36 }
37 double ans=0;
38 void Kruskal(){
39     int i,j;
40     int ti=0;
41     ans=0;
42     for(i=1;i<=cnt;i++){
43         int u=find(e[i].x),v=find(e[i].y);
44         if(u==v)continue;
45         ti++;
46         ans+=e[i].dis;
47         fa[u]=v;
48         if(ti==n-1)break;
49     }
50     return;
51 }
52 int main(){
53     int i,j;
54     while(scanf("%d",&n)!=EOF){
55         init();
56         cnt=0;
57         int u,v,dis;int m;
58         int i,j;
59         for(i=1;i<=n;i++){
60             scanf("%lf%lf",&p[i].x,&p[i].y);
61         }
62         for(i=1;i<n;i++)
63             for(j=i+1;j<=n;j++){
64                 e[++cnt]=(edge){i,j,dist(p[i],p[j])};
65             }
66         sort(e+1,e+cnt+1,cmp);
67         Kruskal();
68         printf("%.2f\n",ans);
69     }
70     return 0;
71 }