hdu 4463 有一条边必须加上 （2012杭州区域赛K题）

耐克店 和 苹果店必须相连

Sample Input
4
2 3
0 0
1 0
0 -1
1 -1
0

Sample Output
3.41

 1 # include <iostream>
 2 # include <cstdio>
 3 # include <cstring>
 4 # include <algorithm>
 5 # include <cmath>
 6 # define LL long long
 7 using namespace std ;
 8
 9 const int INF=0x3f3f3f3f;
10 const int MAXN=110;
11 bool vis[MAXN];
12 double lowc[MAXN];
13 int n ;
14 double cost[MAXN][MAXN] ;
15
16 struct poin
17 {
18     int x ;
19     int y ;
20 }p[MAXN];
21
22 double Prim()//点是0~n-1
23 {
24     double ans=0;
25     memset(vis,false,sizeof(vis));
26     vis[0]=true;
27     for(int i=1;i<n;i++)lowc[i]=cost[0][i];
28     for(int i=1;i<n;i++)
29     {
30         double minc=INF;
31         int p=-1;
32         for(int j=0;j<n;j++)
33             if(!vis[j]&&minc>lowc[j])
34             {
35                 minc=lowc[j];
36                 p=j;
37             }
38             if(minc==INF)return -1;//原图不连通
39             ans+=minc;
40             vis[p]=true;
41             for(int j=0;j<n;j++)
42                 if(!vis[j]&&lowc[j]>cost[p][j])
43                     lowc[j]=cost[p][j];
44     }
45     return ans;
46 }
47
48 int main()
49 {
50
51    // freopen("in.txt","r",stdin) ;
52     while(scanf("%d" , &n) != EOF)
53     {
54         if (n == 0)
55             break ;
56         int i , j ;
57         int pp , qq ;
58         scanf("%d %d" , &pp , &qq) ;
59         for (i = 0 ; i < n ; i++)
60             scanf("%d %d" , &p[i].x , &p[i].y) ;
61         for (i = 0 ; i < n ; i++)
62             for (j = i+1 ; j < n ; j++)
63             {
64                 double t = sqrt((double)(p[i].x - p[j].x) * (p[i].x - p[j].x) + (p[i].y - p[j].y) * (p[i].y - p[j].y)) ;
65                 cost[i][j] = t ;
66                 cost[j][i] = t ;
67             }
68         double k = cost[pp-1][qq-1] ;
69         cost[pp-1][qq-1] = 0 ;
70         cost[qq-1][pp-1] = 0 ;
71         k += Prim() ;
72         printf("%.2lf\n" , k) ;
73
74
75     }
76     return 0 ;
77 }