D - Takahashi Tour https://atcoder.jp/contests/abc213/tasks/abc213_d

abc213_d.py

import sys

sys.setrecursionlimit(10**9)


def dfs(v, visited, ans):
    visited[v] = True
    ans.append(v + 1)
    for u in G[v]:
        if visited[u]:
            continue
        dfs(u, visited, ans)
        ans.append(v + 1)
    return


N = int(input())
G = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(lambda x: int(x) - 1, input().split())
    G[a].append(b)
    G[b].append(a)
for i in range(N):              # 最初、ここがなくてWAが出た。
    G[i].sort()
ans = []
dfs(0, [False] * N, ans)
print(*ans)