Distances

#include <bits/stdc++.h>
using namespace std;

vector< vector<int> > g;

void dfs(int u, int p, int d) {
  if (d % 2 == 0) cout << u << ' ';
  for (auto& v : g[u]) {
    if (v != p) {
      dfs(v, u, d + 1);
    }
  }
  if (d % 2 == 1) cout << u << ' ';
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);  
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    g.assign(n + 1, vector<int>());
    for (int i = 0; i < n - 1; i++) {
      int u, v;
      cin >> u >> v;
      g[u].push_back(v);
      g[v].push_back(u);
    }
    dfs(1, -1, 0);
    cout << '\n';
  }  
  return 0;  
}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 2

Verdict: ACCEPTED