1 /*
2 Source :
3 Problem : 求最近公共祖先的倍增算法
4 Solution :
5 Date :2018-08-16-16.45
6 */
7
8 // #include <bits/stdc++.h>
9 #include<cstdio>
10 #include <cstdlib>
11 #include <cstring>
12 #include <iostream>
13 using namespace std;
14
15 typedef long long LL;
16 const int MAXN = 100005;
17 const LL MOD7 = 1e9+7;
18
19 struct Edge
20 {
21 int u,v;
22 int next;
23 }edge[2*MAXN];
24 int head[MAXN];
25 int cnt;
26 int n;
27
28 void addEdge(int u,int v)
29 {
30 edge[cnt].u=u;edge[cnt].v=v;edge[cnt].next=head[u];head[u]=cnt++;
31 }
32 void init()
33 {
34 memset(head,-1,sizeof(head));
35 cnt=0;
36 }
37
38 int dep[MAXN];
39 int f[MAXN][20];
40
41 void dfs(int u,int pre)
42 {
43 f[u][0]=pre;
44 for (int i=head[u];i!=-1;i=edge[i].next)
45 {
46 int v=edge[i].v;
47 // if (v==pre) continue;
48 dep[v]=dep[u]+1;
49 dfs(v,u);
50 }
51 }
52
53 void BZ()
54 {
55 for (int j=1;j<20;++j)
56 {
57 for (int i=1;i<=n;++i)
58 {
59 if (f[i][j-1])
60 {
61 f[i][j]=f[f[i][j-1]][j-1];
62 }
63 }
64 }
65 }
66
67 int LCA(int u,int v)
68 {
69 if (dep[u]<dep[v]) swap(u,v);
70 int delta = dep[u]-dep[v];
71 for (int i=0;i<20;++i)
72 {
73 if (delta&(1<<i)) u = f[u][i];
74 }
75 if (u==v) return u;
76 for (int i=19;i>=0;--i)
77 {
78 if (f[u][i]!=f[v][i])
79 {
80 u=f[u][i];
81 v=f[v][i];
82 }
83 }
84 return f[u][0];
85 }
86
87 int in[MAXN];
88
89 int main()
90 {
91 #ifndef ONLINE_JUDGE
92 freopen("test.txt","r",stdin);
93 #endif // ONLINE_JUDGE
94 int Case;
95 scanf("%d",&Case);
96 while (Case--)
97 {
98 scanf("%d",&n);
99 init();
100 int u,v;
101 int root=-1;
102 memset(in,0,sizeof(in));
103 for (int i=1;i<n;++i)
104 {
105 scanf("%d%d",&u,&v);
106 addEdge(u,v);
107 in[v]++;
108 // f[v][0]=u;
109 }
110 for (int i=1;i<=n;++i)
111 if (in[i]==0)
112 {
113 root=i;
114 break;
115 }
116 dep[root]=1;
117 dfs(root,0);
118 BZ();
119 int Q;
120 Q=1;
121 for (int i=1;i<=Q;++i)
122 {
123 scanf("%d%d",&u,&v);
124 printf("%d\n",LCA(u,v));
125 }
126 }
127 return 0;
128 }
