2017省夏令营Day8 【bfs，并查集】

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #define Max 2020304
 5 using namespace std;
 6 int n,m,k,s,t,dis[Max],fa[Max],hd,tl,q[Max*2];
 7 int tot,to[Max],next[Max],head[Max];
 8 bool flag,vis[Max];
 9 void add(int x,int y){
10     to[++tot]=y; next[tot]=head[x]; head[x]=tot;
11     to[++tot]=x; next[tot]=head[y]; head[y]=tot;
12 }
13 int find(int x){
14     if(fa[x]==0) return x;
15     return fa[x]=find(fa[x]);
16 }
17 void prework(){
18     flag=true; hd=0; tl=k;
19     memset(fa,0,sizeof(fa));
20     memset(vis,0,sizeof(vis));
21     memset(dis,-1,sizeof(-1));
22     for(int i=1;i<=k;i++) vis[q[i]]=true,dis[q[i]]=0;
23 }
24 void bfs(){
25     prework();
26     while(hd<tl){
27         int vex=q[++hd]; if(!flag) break;
28         for(int i=head[vex];i;i=next[i]){
29             if(!flag) break;
30             int u=find(vex),v=find(to[i]);
31             if(u!=v) fa[u]=v;
32             if(find(s)==find(t)){printf("%d\n",dis[vex]+1); flag=false; break;}
33             if(!vis[to[i]]){
34                 dis[to[i]]=dis[vex]+1;
35                 vis[q[++tl]=to[i]]=true;
36             }
37         }
38     }
39     if(flag) printf("-1\n");
40 }
41 int main()
42 {
43     freopen("masquerade.in","r",stdin);
44     freopen("masquerade.out","w",stdout);
45     int T; scanf("%d",&T);
46     while(T--){
47         memset(head,tot=0,sizeof(head));
48         memset(to,0,sizeof(to));
49         memset(next,0,sizeof(next));
50         scanf("%d%d%d",&n,&m,&k);
51         for(int i=1;i<=k;i++) scanf("%d",&q[i]);
52         int now=n;
53         for(int i=1;i<=m;i++){
54             int x,y; scanf("%d%d",&x,&y);
55             add(x,++now); add(now,y);
56         }
57         scanf("%d%d",&s,&t); q[++k]=t;
58         bfs();
59     }
60 }