Distances

#include <iostream>
#include <cstdio>
#include <vector>
#include <queue>
#include <fstream>
#include <bitset>
#include <cassert>
#include <functional>
#include <cstring>
#include <ctime>
#include <cmath>
#include <set>
#include <map>
#include <algorithm>
#define sec second
#define fir first
#define pb push_back
#define mp make_pair
#define REP(i , n) for (int i = 0 ; i < (n) ; i++)
#define BACK(i , n) for (int i = (n) - 1 ; i >= 0 ; i--)
using namespace std;
using vi = vector<int>;
using vii = vector<vi>;
using pii = pair<int , int>;
using ll = long long;
using ld = long double;
const int MAX = 1e9 , MIN = - MAX , MOD = 1e9 + 7;
const ll MAX_LL = 1e18 , MIN_LL = -MAX_LL;
void dfs(int node , int bef , int depth , vector<int> adjl[]){
    if (depth % 3 == 0)
        cout << node << ' ';
    for (int it : adjl[node])
        if (it != bef)
            dfs(it , node , depth + 1 , adjl);
    if (depth % 3 != 0)
        cout << node << ' ';
}
int main(){
    int T;
    cin >> T;
    while(T--){
        int N;
        cin >> N;
        vector<int> adjl[N + 1];
        REP(i , N - 1){
            int a , b;
            cin >> a >> b;
            adjl[a].push_back(b);
            adjl[b].push_back(a);
        }
        dfs(1 , -1 , 0 , adjl);
        cout << endl;
    }
}

Test 1

Group: 1, 2

Verdict: WRONG ANSWER

Test 2

Group: 2

Verdict: WRONG ANSWER