python/TangDou/Topic/HuanGenDp/CF1406C.cpp

#include <bits/stdc++.h>
#define N 100005
using namespace std;
int n, head[N], ver[2 * N], Next[2 * N], tot = 0;
void add(int x, int y) {
    ver[++tot] = y, Next[tot] = head[x], head[x] = tot;
}
vector<int> c;
int mx[N], sz[N];
int mn = 0x3f3f3f3f;
void dfs(int x, int pre) {
    for (int i = head[x]; i; i = Next[i]) {
        int y = ver[i];
        if (y == pre) continue;
        dfs(y, x);
        sz[x] += (sz[y] + 1);
        mx[x] = max(mx[x], sz[y] + 1);
    }
    mx[x] = max(mx[x], n - 1 - sz[x]);
    mn = min(mn, mx[x]);
}
void solve() {
    cin >> n;
    tot = 0;
    mn = 0x3f3f3f3f;
    c.clear();
    for (int i = 0; i <= n; i++) {
        head[i] = 0;
        mx[i] = 0;
        sz[i] = 0;
    }
    for (int i = 1; i < n; i++) {
        int x, y;
        cin >> x >> y;
        add(x, y);
        add(y, x);
    }
    dfs(1, 0);
    for (int i = 1; i <= n; i++) {
        if (mx[i] == mn) {
            c.push_back(i);
        }
    }
    if (c.size() == 1) {
        for (int i = head[c[0]]; i; i = Next[i]) {
            int y = ver[i];
            cout << c[0] << " " << y << endl;
            cout << c[0] << " " << y << endl;
            return;
        }
    } else {
        int tmp;
        for (int i = head[c[0]]; i; i = Next[i]) {
            int y = ver[i];
            if (y == c[1]) continue;
            cout << c[0] << " " << y << endl;
            tmp = y;
            break;
        }
        cout << c[1] << " " << tmp << endl;
        return;
    }
}
int main() {
    int T;
    cin >> T;
    while (T--) {
        solve();
    }
    return 0;
}