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#include <bits/stdc++.h>
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using namespace std;
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const int N = 1e5 + 10, M = N << 1;
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#define int long long
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#define endl "\n"
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// 链式前向星
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int e[M], h[N], idx, w[M], ne[M];
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void add(int a, int b, int c = 0) {
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e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
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}
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vector<int> g[N]; // 邻接表，存图
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int sz[N]; // sz[i]:以i为根的子树中节点个数
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int son[N]; // son[i]:去掉节点i后，剩下的连通分量中最大子树节点个数
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int r1, r2, n;
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void dfs(int u, int fa) {
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sz[u] = 1; // u为根的子树中，最起码有一个节点u
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son[u] = 0; // 把节点u去掉后，剩下的连通分量中最大子树节点个数现在还不知道，预求最大，先设最小
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// for (int i = 0; i < g[u].size(); i++) { // 枚举u的每一条出边
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for (int i = h[u]; ~i; i = ne[i]) {
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// int v = g[u][i];
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int v = e[i];
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if (v == fa) continue;
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dfs(v, u);
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sz[u] += sz[v];
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son[u] = max(son[u], sz[v]);
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}
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son[u] = max(son[u], n - sz[u]);
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if ((son[u] << 1) <= n) r2 = r1, r1 = u;
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}
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/*
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1 2
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1 2
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1 3
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2 3
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*/
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signed main() {
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#ifndef ONLINE_JUDGE
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freopen("CF1406C.in", "r", stdin);
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#endif
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int T;
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cin >> T;
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while (T--) {
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cin >> n;
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// 多组测试数据，清空
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memset(sz, 0, sizeof sz);
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memset(son, 0, sizeof son);
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// 初始化链式前向星
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memset(h, -1, sizeof h);
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idx = 0;
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r1 = r2 = 0;
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for (int i = 0; i <= n + 10; i++) g[i].clear();
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for (int i = 1; i < n; i++) { // n-1条边
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int x, y;
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cin >> x >> y;
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g[x].push_back(y);
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g[y].push_back(x);
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add(x, y), add(y, x);
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}
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dfs(1, 0); // 以1号点为入口，它的父节点是0
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if (!r2) {
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int r3 = g[r1][0];
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cout << r1 << " " << r3 << endl;
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cout << r1 << " " << r3 << endl;
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} else {
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int r3 = r1;
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for (int i = 0; i < g[r2].size(); i++) {
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r3 = g[r2][i];
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if (r3 != r1) break;
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}
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cout << r3 << " " << r2 << endl;
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cout << r3 << " " << r1 << endl;
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}
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}
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return 0;
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} |
