Buggy python submission (verdict: Runtime Error):
N = int(input())
T = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)


colors = [-1] * N
stack = [(0, 0)]
while stack:
    n, color = stack.pop()
    colors[n] = color
    for to in T[n]:
        if colors[to] != -1:
            continue
        stack.append((to, color ^ 1))


# あまり１、あまり２、あまり０になるように並び替え
X = [[] for _ in range(3)]
for n in range(1, N + 1):
    X[n % 3].append(n)
X.append(X[0])
del X[0]


ans = []
x12, x3 = X[0] + X[1], X[2]
if colors.count(0) <= N // 3:
    for color in colors:
        if color == 0:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

elif colors.count(1) <= N // 3:
    for color in colors:
        if color == 1:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

else:
    for color in colors:
        if X[color]:
            ans.append(X[color ^ 1].pop())
        else:
            ans.append(X[2].pop())

print(' '.join(map(str, ans)))


Fixed submission:
N = int(input())
T = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)


colors = [-1] * N
stack = [(0, 0)]
while stack:
    n, color = stack.pop()
    colors[n] = color
    for to in T[n]:
        if colors[to] != -1:
            continue
        stack.append((to, color ^ 1))


# あまり１、あまり２、あまり０になるように並び替え
X = [[] for _ in range(3)]
for n in range(1, N + 1):
    X[n % 3].append(n)
X.append(X[0])
del X[0]


ans = []
x12, x3 = X[0] + X[1], X[2]
if colors.count(0) <= N // 3:
    for color in colors:
        if color == 0:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

elif colors.count(1) <= N // 3:
    for color in colors:
        if color == 1:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

else:
    for color in colors:
        if X[color]:
            ans.append(X[color].pop())
        else:
            ans.append(X[2].pop())

print(' '.join(map(str, ans)))

Buggy python submission (verdict: Runtime Error):
N = int(input())
T = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)


colors = [-1] * N
stack = [(0, 0)]
while stack:
    n, color = stack.pop()
    colors[n] = color
    for to in T[n]:
        if colors[to] != -1:
            continue
        stack.append((to, color ^ 1))


# あまり１、あまり２、あまり０になるように並び替え
X = [[] for _ in range(3)]
for n in range(1, N + 1):
    X[n % 3].append(n)
X.append(X[0])
del X[0]


# 少ない色の方は優先的に３の倍数を使うようにして塗る
ans = []
for color in colors:
    if X[color ^ 1]:
        ans.append(X[color ^ 1].pop())
    else:
        ans.append(X[2].pop())

print(' '.join(map(str, ans)))


Fixed submission:
N = int(input())
T = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)


colors = [-1] * N
stack = [(0, 0)]
while stack:
    n, color = stack.pop()
    colors[n] = color
    for to in T[n]:
        if colors[to] != -1:
            continue
        stack.append((to, color ^ 1))


# あまり１、あまり２、あまり０になるように並び替え
X = [[] for _ in range(3)]
for n in range(1, N + 1):
    X[n % 3].append(n)
X.append(X[0])
del X[0]


ans = []
x12, x3 = X[0] + X[1], X[2]
if colors.count(0) <= N // 3:
    for color in colors:
        if color == 0:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

elif colors.count(1) <= N // 3:
    for color in colors:
        if color == 1:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

else:
    for color in colors:
        if X[color]:
            ans.append(X[color].pop())
        else:
            ans.append(X[2].pop())

print(' '.join(map(str, ans)))

Buggy python submission (verdict: Runtime Error):
N = int(input())
T = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)


colors = [-1] * N
stack = [(0, 0)]
while stack:
    n, color = stack.pop()
    colors[n] = color
    for to in T[n]:
        if colors[to] != -1:
            continue
        stack.append((to, color ^ 1))


# あまり１、あまり２、あまり０になるように並び替え
X = [[] for _ in range(3)]
for n in range(1, N + 1):
    X[n % 3].append(n)
X.append(X[0])
del X[0]


ans = []
for color in colors:
    if X[color]:
        ans.append(X[color].pop())
    else:
        ans.append(X[2].pop())

print(' '.join(map(str, ans)))


Fixed submission:
N = int(input())
T = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)


colors = [-1] * N
stack = [(0, 0)]
while stack:
    n, color = stack.pop()
    colors[n] = color
    for to in T[n]:
        if colors[to] != -1:
            continue
        stack.append((to, color ^ 1))


# あまり１、あまり２、あまり０になるように並び替え
X = [[] for _ in range(3)]
for n in range(1, N + 1):
    X[n % 3].append(n)
X.append(X[0])
del X[0]


ans = []
x12, x3 = X[0] + X[1], X[2]
if colors.count(0) <= N // 3:
    for color in colors:
        if color == 0:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

elif colors.count(1) <= N // 3:
    for color in colors:
        if color == 1:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

else:
    for color in colors:
        if X[color]:
            ans.append(X[color].pop())
        else:
            ans.append(X[2].pop())

print(' '.join(map(str, ans)))

Buggy python submission (verdict: Runtime Error):
from collections import deque
N = int(input())
T = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)

x1, x2, x3 = [], [], []
for n in range(1, N + 1):
    if n % 3 == 1:
        x1.append(n)

    elif n % 3 == 2:
        x2.append(n)

    elif n % 3 == 0:
        x3.append(n)


ans = [-1] * N


def allocate(i, pop_target):
    if pop_target == 1:
        if x1:
            ans[i] = x1.pop()
        else:
            ans[i] = x3.pop()

    else:
        if x2:
            ans[i] = x2.pop()
        else:
            ans[i] = x3.pop()


def bfs(s):
    que = deque([(s, 0)])
    pop_target = 1 if len(x1) >= len(x2) else 2

    while que:
        n, depth = que.pop()
        if depth == 2:
            continue

        allocate(n, pop_target)
        for to in T[n]:
            if ans[to] > 0:
                continue
            que.appendleft((to, depth + 1))


for n in range(N):
    if ans[n] > 0:
        continue
    bfs(n)

print(*ans, sep=' ')


Fixed submission:
N = int(input())
T = [[] for _ in range(N)]
for _ in range(N - 1):
    a, b = map(int, input().split())
    a, b = a - 1, b - 1
    T[a].append(b)
    T[b].append(a)


colors = [-1] * N
stack = [(0, 0)]
while stack:
    n, color = stack.pop()
    colors[n] = color
    for to in T[n]:
        if colors[to] != -1:
            continue
        stack.append((to, color ^ 1))


# あまり１、あまり２、あまり０になるように並び替え
X = [[] for _ in range(3)]
for n in range(1, N + 1):
    X[n % 3].append(n)
X.append(X[0])
del X[0]


ans = []
x12, x3 = X[0] + X[1], X[2]
if colors.count(0) <= N // 3:
    for color in colors:
        if color == 0:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

elif colors.count(1) <= N // 3:
    for color in colors:
        if color == 1:
            ans.append(x3.pop())
        elif x12:
            ans.append(x12.pop())
        else:
            ans.append(x3.pop())

else:
    for color in colors:
        if X[color]:
            ans.append(X[color].pop())
        else:
            ans.append(X[2].pop())

print(' '.join(map(str, ans)))