Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black > n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
sys.setrecursionlimit(10000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
sys.setrecursionlimit(10000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

color = [0] * (n+1) #color[i]:点iの色(1 or -1)。但し塗られていないときは0とする

def f(v,c):
    #頂点vに隣接する頂点全てを塗るあるいは判定する
    color[v] = c
    for i in range(len(g[v])):
        if color[ g[v][i] ] == 0:
            f(g[v][i],-c)
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
res = f(i,1)
black = 0
for i in color[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if color[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if color[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)
"""#親のノードに子を入れてくdfs
stack = [1]
parent = [0]*(n+1)
order = []
while stack:
    x = stack.pop()
    order.append(x)
    for i in g[x]:
        if i == parent[x]:
            continue
        parent[i] = x
        stack.append(i)"""
color = [0] * (n+1) #color[i]:点iの色(1 or -1)。但し塗られていないときは0とする

def f(v,c):
    #頂点vに隣接する頂点全てを塗るあるいは判定する
    color[v] = c
    for i in range(len(g[v])):
        if color[ g[v][i] ] == c:
            return False
        elif color[ g[v][i] ] == 0 and not f(g[v][i],-c):
            #(g[v][i]がまだ塗られていない　かつ　そこを-cで塗っても問題ない) ではないなら
            return False
    return True
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
res = f(i,1)
black = 0
for i in color[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if color[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if color[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
sys.setrecursionlimit(100000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)
"""#親のノードに子を入れてくdfs
stack = [1]
parent = [0]*(n+1)
order = []
while stack:
    x = stack.pop()
    order.append(x)
    for i in g[x]:
        if i == parent[x]:
            continue
        parent[i] = x
        stack.append(i)"""
color = [0] * (n+1) #color[i]:点iの色(1 or -1)。但し塗られていないときは0とする

def f(v,c):
    #頂点vに隣接する頂点全てを塗るあるいは判定する
    color[v] = c
    for i in range(len(g[v])):
        if color[ g[v][i] ] == c:
            return False
        elif color[ g[v][i] ] == 0 and not f(g[v][i],-c):
            #(g[v][i]がまだ塗られていない　かつ　そこを-cで塗っても問題ない) ではないなら
            return False
    return True
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
res = f(i,1)
black = 0
for i in color[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if color[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if color[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)
"""#親のノードに子を入れてくdfs
stack = [1]
parent = [0]*(n+1)
order = []
while stack:
    x = stack.pop()
    order.append(x)
    for i in g[x]:
        if i == parent[x]:
            continue
        parent[i] = x
        stack.append(i)"""
color = [0] * (n+1) #color[i]:点iの色(1 or -1)。但し塗られていないときは0とする

def f(v,c):
    #頂点vに隣接する頂点全てを塗るあるいは判定する
    color[v] = c
    for i in range(len(g[v])):
        if color[ g[v][i] ] == c:
            return False
        elif color[ g[v][i] ] == 0 and not f(g[v][i],-c):
            #(g[v][i]がまだ塗られていない　かつ　そこを-cで塗っても問題ない) ではないなら
            return False
    return True
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
res = f(i,1)
black = 0
for i in color[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if color[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if color[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)
"""#親のノードに子を入れてくdfs
stack = [1]
parent = [0]*(n+1)
order = []
while stack:
    x = stack.pop()
    order.append(x)
    for i in g[x]:
        if i == parent[x]:
            continue
        parent[i] = x
        stack.append(i)"""
color = [0] * (n+1) #color[i]:点iの色(1 or -1)。但し塗られていないときは0とする

def f(v,c):
    #頂点vに隣接する頂点全てを塗るあるいは判定する
    color[v] = c
    for i in range(len(g[v])):
        if color[ g[v][i] ] == c:
            return False
        elif color[ g[v][i] ] == 0 and not f(g[v][i],-c):
            #(g[v][i]がまだ塗られていない　かつ　そこを-cで塗っても問題ない) ではないなら
            return False
    return True
ans = [0]*(n+1)
t0 = deque([i*3 for i in range(1,n//2)])
t1 = deque([1+i*3 for i in range(0,n//2-1)])
t2 = deque([2+i*3 for i in range(0,n//2-1)])
res = f(i,1)
black = 0
for i in color[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if color[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if color[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)
 
color = [0] * (n+1) #color[i]:点iの色(1 or -1)。但し塗られていないときは0とする

def f(v,c):
    #頂点vに隣接する頂点全てを塗るあるいは判定する
    color[v] = c
    for i in range(len(g[v])):
        if color[ g[v][i] ] == c:
            return False
        elif color[ g[v][i] ] == 0 and not f(g[v][i],-c):
            #(g[v][i]がまだ塗られていない　かつ　そこを-cで塗っても問題ない) ではないなら
            return False
    return True
ans = [0]*(n+1)
t0 = deque([i*3 for i in range(1,n//2)])
t1 = deque([1+i*3 for i in range(0,n//2)])
t2 = deque([2+i*3 for i in range(0,n//2)])
for i in range(n):
    if color[i] == 0:
        res = f(i,1)
black = 0
for i in color[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if color[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if color[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque
readline = sys.stdin.buffer.readline
n = int(readline())

graph = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    graph[a].append(b)
    graph[b].append(a)
 
#親のノードに子を入れてくdfs
AB = []
def bfs(i): #長さ3までi=3まで
    queue = deque([[i,0]])
    visited = []
    while queue:
        x,l = queue.popleft()
        if l < 3:
            for j in graph[x]:
                if not j in visited:
                    queue.append([j,l+1])
            visited.append(x)
        else:
            if i < x:
                AB.append([i,x])
            visited.append(x)
for i in range(1,n+1):
    bfs(i)
graph = [[] for _ in range(n+1)] #隣接リスト
for a,b in AB:
    graph[a].append(b)
    graph[b].append(a)

#親のノードに子を入れてくdfs
stack = [AB[0][0]] #グラフに組み込まれた適当な値を入れる
parent = [0]*(n+1)
order = []
while stack:
    x = stack.pop()
    order.append(x)
    for i in graph[x]:
        if i == parent[x]:
            continue
        parent[i] = x
        stack.append(i)

ans = [0]*(n+1)

t0 = deque([i*3 for i in range(1,n//2)])
t1 = deque([1+i*3 for i in range(0,n//2)])
t2 = deque([2+i*3 for i in range(0,n//2)])

for x in order: #親
    if parent[x] == 0:
        ans[x] = t1.pop()
    else:
        if ans[parent[x]]%3 == 0: #ans[parent[x]] != 0 and ←決まってる？
            if len(t1)!=0:
                ans[x] = t1.pop()
            elif len(t2)!=0:
                ans[x] = t2.pop()
            elif len(t0) != 0:
                ans[x] = t0.pop()
        elif ans[parent[x]]%3 == 1:
            if len(t2) != 0:
                ans[x] = t2.pop()
            elif len(t0) != 0:
                ans[x] = t0.pop()
            else:
                print(-1)
                exit()
        else:
            if len(t1) != 0:
                ans[x] = t1.pop()
            elif len(t0) != 0:
                ans[x] = t0.pop()
            else:
                print(-1)
                exit()

nokori = t0+t1+t2
j = 0
for i in range(1,n+1):
    if ans[i] == 0:
        ans[i] = nokori[j]
        j += 1
print(*ans[1:])

Fixed submission:
import sys
from collections import deque
sys.setrecursionlimit(1000000)
readline = sys.stdin.buffer.readline
n = int(readline())

g = [[] for _ in range(n+1)] #隣接リスト
for i in range(n-1):
    a,b = map(int,readline().split())
    g[a].append(b)
    g[b].append(a)

colors = [0] * (n+1)
 
colors[1] = 1
 
todo = []
for to in g[1]:
    todo.append([to, -1])
 
while todo:
    node, color = todo.pop()
 
    if colors[node] != 0:
        continue
 
    colors[node] = color
    new_color = -color
    for to in g[node]:
        if colors[to] != 0:
            continue
        todo.append([to, new_color])
ans = [0]*(n+1)
t0 = deque([])
t1 = deque([])
t2 = deque([])
for i in range(1,n+1):
    if i%3==1:
        t1.append(i)
    elif i%3==2:
        t2.append(i)
    else:
        t0.append(i)
black = 0
for i in colors[1:]:
    if i == 1:
        black += 1

if black <= n//3:
    for i in range(1,n+1):
        if colors[i] == 1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
elif black >= n-n//3:
    for i in range(1,n+1):
        if colors[i] == -1:
            ans[i] = t0.pop()
        else:
            if t1:
                ans[i] = t1.pop()
            elif t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
else:
    for i in range(1,n+1):
        if colors[i] == 1:
            if t1:
                ans[i] = t1.pop()
            else:
                ans[i] = t0.pop()
        else:
            if t2:
                ans[i] = t2.pop()
            else:
                ans[i] = t0.pop()
print(*ans[1:])