题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4463
很裸的一道题目，稍微处理一下输入即可
代码：
1 #include<iostream> 2 #include<cstdlib> 3 #include<cstdio> 4 #include<cstring> 5 #include<cmath> 6 #include<algorithm> 7 using namespace std; 8 #define maxn 60 9 int n; 10 double sumweight; 11 int tol; 12 int cnt; 13 int p,q; 14 class node 15 { 16 public: 17 int from; 18 int to; 19 double w; 20 }; 21 class point 22 { 23 public: 24 int x; 25 int y; 26 }; 27 point address[maxn]; 28 node edge[maxn*maxn]; 29 int parent[maxn*maxn]; 30 double dis(point a,point b) 31 { 32 return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)); 33 } 34 void addEdge(int u,int v) 35 { 36 edge[tol].from=u; 37 edge[tol].to=v; 38 edge[tol].w=dis(address[u],address[v]); 39 if((u==p && v==q)||(u==q && v==p)) 40 edge[tol].w=0; 41 tol++; 42 } 43 void UFset() 44 { 45 for(int i=0;i<maxn*maxn;i++) 46 parent[i]=-1; 47 } 48 int Find(int x) 49 { 50 int s; 51 for(s=x;parent[s]>=0;s=parent[s]);//我总是把parent[s]>=0 写为s>=0; 52 while(s!=x) 53 { 54 int tmp=parent[x]; 55 parent[x]=s; 56 x=tmp; 57 } 58 59 return s; 60 } 61 void Union(int u,int v) 62 { 63 int r1=Find(u); 64 int r2=Find(v); 65 int tmp=parent[r1]+parent[r2]; 66 if(parent[r1]>parent[r2]) 67 { 68 parent[r1]=r2; 69 parent[r2]=tmp; 70 } 71 else 72 { 73 parent[r2]=r1; 74 parent[r1]=tmp; 75 } 76 } 77 bool cmp(node a ,node b) 78 { 79 return a.w < b.w; 80 } 81 void Kruskal() 82 { 83 int u,v; 84 UFset(); 85 cnt=0; 86 for(int i=0;i<tol;i++) 87 { 88 u=edge[i].from; 89 v=edge[i].to; 90 if(Find(u)!= Find(v)) 91 { 92 sumweight+=edge[i].w; 93 cnt++; 94 Union(u,v); 95 if(cnt==n-1) break; 96 } 97 } 98 99 } 100 int main() 101 { 102 while(scanf("%d",&n)&&n) 103 { 104 tol=0; 105 106 scanf("%d%d",&p,&q); 107 int x,y; 108 for(int i=1;i<=n;i++) 109 { 110 scanf("%d%d",&x,&y); 111 address[i].x=x; 112 address[i].y=y; 113 } 114 for(int i=1;i<=n;i++) 115 for(int j=i+1;j<=n;j++) 116 { 117 addEdge(i,j); 118 } 119 sumweight=dis(address[p],address[q]); 120 sort(edge,edge+tol,cmp); 121 Kruskal(); 122 printf("%.2f ",sumweight); 123 124 125 126 } 127 128 129 return 0; 130 }