HDU-1232 畅通工程 （并查集、判断图中树的棵数）

 1 # include<iostream>
 2 # include<cstdio>
 3 # include<cstring>
 4 # include<vector>
 5 # include<set>
 6 # include<vector>
 7 # include<algorithm>
 8 using namespace std;
 9 int n,m;
10 int pre[1005];
11 struct edge
12 {
13     int v1,v2;
14 };
15 vector<edge>e;
16 int find(int x)
17 {
18     if(pre[x]==x)
19         return x;
20     return pre[x]=find(pre[x]);
21     /*int u=x;
22     while(u!=pre[u])
23         u=pre[u];
24     while(x!=pre[x]){
25         int v=x;
26         x=pre[x];
27         pre[v]=u;
28     }
29     return u;*/
30 }
31 void solve(int v1,int v2)
32 {
33 
34     //for(int i=0;i<e.size();++i){
35         int u=find(v1);
36         int v=find(v2);
37         if(u!=v)
38             pre[u]=v;
39     //}
40     /*for(int i=0;i<e.size();++i){
41         int u=find(e[i].v1);
42         int v=find(e[i].v2);
43         if(u!=v)
44             pre[u]=v;
45     }*/
46 }
47 int main()
48 {
49     int a,b;
50     while(scanf("%d",&n)&&n)
51     {
52         for(int i=1;i<=n;++i)
53             pre[i]=i;
54         scanf("%d",&m);
55         while(m--){
56             scanf("%d%d",&a,&b);
57             //if(!mark[a][b]){
58             solve(a,b);
59                 //mark[a][b]=mark[b][a]=1;
60             //}
61         }
62         int num=0;
63         for(int i=1;i<=n;++i)
64             if(pre[i]==i)
65                 ++num;
66         printf("%d\n",num-1);
67     }
68     return 0;
69 }