Nearest Common Ancestors·POJ1330

 1 #include<set>
 2 #include<queue>
 3 #include<vector>
 4 #include<cstdio>
 5 #include<cstring>
 6 #include<iostream>
 7 #include<algorithm>
 8 using namespace std;
 9 const int N = 10010;
10 #define For(i,n) for(int i=1;i<=n;i++)
11 #define Rep(i,l,r) for(int i=l;i<=r;i++)
12 
13 struct Edge{
14     int t,next;
15 }E[N];
16 
17 int in[N],head[N],Es;
18 int n,T,x,y,ans,qx,qy,root,anc[N],fa[N];
19 bool vis[N];
20 
21 void makelist(int s,int t){
22     E[Es].t = t;E[Es].next = head[s];
23     head[s] = Es++;
24 }
25 
26 int find(int i){
27     return (fa[i]==i)?(i):(find(fa[i]));
28 }
29 
30 void LCA(int i){
31     if(ans!=0) return;
32     anc[i] = i;
33     for(int p = head[i];p!=-1;p=E[p].next){
34         LCA(E[p].t);
35         fa[find(E[p].t)] = find(i);
36         anc[find(i)] = i;
37     }
38     vis[i] = true;
39     if(i==qx)
40         if(vis[qy]) ans = anc[find(qy)];
41     if(i==qy)
42         if(vis[qx]) ans = anc[find(qx)];
43 }
44 
45 int main(){
46     scanf("%d",&T);
47     For(i,T){
48         memset(head,-1,sizeof(head));Es = 0;ans = 0;
49         memset(in,0,sizeof(in));memset(anc,0,sizeof(anc));
50         memset(vis,false,sizeof(vis));
51         scanf("%d",&n);
52         For(i,n-1){
53             fa[i] = i;
54             scanf("%d %d",&x,&y);
55             makelist(x,y);
56             in[y]++;
57         }
58         fa[n] = n;
59         For(i,n)
60             if(!in[i]) {root = i;break;}
61         scanf("%d %d",&qx,&qy);
62         LCA(root);
63         printf("%d\n",ans);
64     }
65     return 0;
66 }