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| #include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#define ll long long
#define maxn 100010
#define cn const node
#define cQ const Queue
#define INF 1000000000000000000ll
using namespace std;
int n, m;
struct Edge {
int fr, to, next;
} e[maxn * 2]; int c1, head[maxn];
inline void add_edge(int u, int v) {
e[c1].fr = u; e[c1].to = v;
e[c1].next = head[u]; head[u] = c1++;
}
int f[maxn], sz[maxn];
void dfs(int u, int fa) {
sz[u] = 1; f[u] = 0;
for (int i = head[u]; ~i; i = e[i].next) {
int v = e[i].to; if (v == fa) continue ;
dfs(v, u); sz[u] += sz[v]; f[u] = max(f[u], sz[v]);
}
f[u] = max(f[u], n - sz[u]);
}
int ans1, ans2;
void Dfs(int u, int fa) {
bool F = 1;
for (int i = head[u]; ~i; i = e[i].next) {
int v = e[i].to; if (v == fa) continue ;
Dfs(v, u); F = 0;
}
if (F) ans1 = fa, ans2 = u;
}
void clear() {
for (int i = 1; i <= n; ++i) head[i] = -1; c1 = 0;
}
void work() {
cin >> n;
for (int i = 1; i < n; ++i) {
int x, y; cin >> x >> y;
add_edge(x, y); add_edge(y, x);
}
if (n & 1) {
cout << e[1].fr << " " << e[1].to << endl;
cout << e[1].fr << " " << e[1].to << endl;
return clear();
} dfs(1, 0); int p1 = 0, p2 = 0, s = 0;
for (int i = 1; i <= n; ++i) {
if (f[i] < n / 2) continue;
if (f[i] == n / 2 && p1) p2 = i;
else if (f[i] == n / 2) p1 = i;
++s;
}
if (p1 && p2 && s == n) {
Dfs(p2, p1);
cout << ans1 << " " << ans2 << endl;
cout << ans2 << " " << p1 << endl;
clear();
}
else {
cout << e[1].fr << " " << e[1].to << endl;
cout << e[1].fr << " " << e[1].to << endl;
clear();
}
}
int main() {
int T; cin >> T; memset(head, -1, sizeof head);
while (T--) work();
return 0;
}
|