Buggy python submission (verdict: Runtime Error):
N = int(input())
ab = [list(map(int,input().split())) for _ in range(N-1)]
from collections import deque
l = [deque() for _ in range(N+1)]
ans = [0]*N
for a,b in ab:
  l[a].append(b)
  l[b].append(a)
  
r = [0]*(N+1)
i = 0
p = l[1]
q = deque()
flag = [False]*(N+1)
flag[1]=True
while (len(p)!=0)or(len(q)!=0):
  if i%2==0:
    while len(p)!=0:
      j = p.pop()
      if flag[j]:
        continue
      else:
        q.extend(l[j])
        flag[j]=True
        r[j]=1
    i+=1
  else:
    while len(q)!=0:
      j = q.pop()
      if flag[j]:
        continue
      else:
        p.extend(l[j])
        flag[j]=True
    i+=1
a = deque(range(1,N+1,3))
b = deque(range(2,N+1,3))
c = deque(range(3,N+1,3))
x = sum(r)
if x<=N//3:
  for i in range(1,N+1):
    if r[i]==1:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      else:
        ans[i-1]=b.pop()
elif (N-x)<=N//3:
  for i in range(1,N+1):
    if r[i]==0:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(b)!=0:
        ans[i-1]=b.pop()
else:
  for i in range(1,N+1):
    if r[i]==1:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(c)!=0:
        ans[i-1]=c.pop()
      else:
        ans[i-1]=b.pop()
    else:
      if len(b)!=0:
        ans[i-1]=b.pop()
      elif len(c)!=0:
        ans[i-1]=c.pop()
      else:
        ans[i-1]=a.pop()
        
print(' '.join(map(str,ans)))

Fixed submission:
N = int(input())
ab = [list(map(int,input().split())) for _ in range(N-1)]
from collections import deque
l = [deque() for _ in range(N+1)]
ans = [0]*N
for a,b in ab:
  l[a].append(b)
  l[b].append(a)
  
r = [0]*(N+1)
i = 0
p = l[1]
q = deque()
flag = [False]*(N+1)
flag[1]=True
while (len(p)!=0)or(len(q)!=0):
  if i%2==0:
    while len(p)!=0:
      j = p.pop()
      if flag[j]:
        continue
      else:
        q.extend(l[j])
        flag[j]=True
        r[j]=1
    i+=1
  else:
    while len(q)!=0:
      j = q.pop()
      if flag[j]:
        continue
      else:
        p.extend(l[j])
        flag[j]=True
    i+=1
a = deque(range(1,N+1,3))
b = deque(range(2,N+1,3))
c = deque(range(3,N+1,3))
x = sum(r)
if x<=N//3:
  for i in range(1,N+1):
    if r[i]==1:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(b)!=0:
        ans[i-1]=b.pop()
      else:
        ans[i-1]=c.pop()
elif (N-x)<=N//3:
  for i in range(1,N+1):
    if r[i]==0:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(b)!=0:
        ans[i-1]=b.pop()
      else:
        ans[i-1]=c.pop()
else:
  for i in range(1,N+1):
    if r[i]==1:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(c)!=0:
        ans[i-1]=c.pop()
      else:
        ans[i-1]=b.pop()
    else:
      if len(b)!=0:
        ans[i-1]=b.pop()
      elif len(c)!=0:
        ans[i-1]=c.pop()
      else:
        ans[i-1]=a.pop()
        
print(' '.join(map(str,ans)))

Buggy python submission (verdict: Runtime Error):
N = int(input())
ab = [list(map(int,input().split())) for _ in range(N-1)]
from collections import deque
l = [deque() for _ in range(N+1)]
ans = [0]*N
for a,b in ab:
  l[a].append(b)
  l[b].append(a)
  
r = [0]*(N+1)
i = 0
p = l[1]
q = deque()
flag = [False]*(N+1)
flag[1]=True
while (len(p)!=0)or(len(q)!=0):
  if i%2==0:
    while len(p)!=0:
      j = p.pop()
      if flag[j]:
        continue
      else:
        q.extend(l[j])
        flag[j]=True
        r[j]=1
    i+=1
  else:
    while len(q)!=0:
      j = q.pop()
      if flag[j]:
        continue
      else:
        p.extend(l[j])
        flag[j]=True
    i+=1
a = deque(range(1,N+1,3))
b = deque(range(2,N+1,3))
c = deque(range(3,N+1,3))
x = sum(r)
if x<=N//3:
  for i in range(1,N+1):
    if r[i]==1:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      else:
        ans[i-1]=b.pop()
elif (N-x)<=N//3:
  for i in range(1,N+1):
    if r[i]==0:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(b)!=0:
        ans[i-1]=b.pop()
else:
  for i in range(1,N+1):
    if r[i]==1:
      if len(a)!=0:
        ans[i-1]=a.pop()
      else:
        ans[i-1]=c.pop()
    else:
      if len(b)!=0:
        ans[i-1]=b.pop()
      else:
        ans[i-1]=c.pop()
        
print(' '.join(map(str,ans)))

Fixed submission:
N = int(input())
ab = [list(map(int,input().split())) for _ in range(N-1)]
from collections import deque
l = [deque() for _ in range(N+1)]
ans = [0]*N
for a,b in ab:
  l[a].append(b)
  l[b].append(a)
  
r = [0]*(N+1)
i = 0
p = l[1]
q = deque()
flag = [False]*(N+1)
flag[1]=True
while (len(p)!=0)or(len(q)!=0):
  if i%2==0:
    while len(p)!=0:
      j = p.pop()
      if flag[j]:
        continue
      else:
        q.extend(l[j])
        flag[j]=True
        r[j]=1
    i+=1
  else:
    while len(q)!=0:
      j = q.pop()
      if flag[j]:
        continue
      else:
        p.extend(l[j])
        flag[j]=True
    i+=1
a = deque(range(1,N+1,3))
b = deque(range(2,N+1,3))
c = deque(range(3,N+1,3))
x = sum(r)
if x<=N//3:
  for i in range(1,N+1):
    if r[i]==1:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(b)!=0:
        ans[i-1]=b.pop()
      else:
        ans[i-1]=c.pop()
elif (N-x)<=N//3:
  for i in range(1,N+1):
    if r[i]==0:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(b)!=0:
        ans[i-1]=b.pop()
      else:
        ans[i-1]=c.pop()
else:
  for i in range(1,N+1):
    if r[i]==1:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(c)!=0:
        ans[i-1]=c.pop()
      else:
        ans[i-1]=b.pop()
    else:
      if len(b)!=0:
        ans[i-1]=b.pop()
      elif len(c)!=0:
        ans[i-1]=c.pop()
      else:
        ans[i-1]=a.pop()
        
print(' '.join(map(str,ans)))

Buggy python submission (verdict: Runtime Error):
N = int(input())
ab = [list(map(int,input().split())) for _ in range(N-1)]
from collections import deque
l = [deque() for _ in range(N+1)]
ans = [0]*N
for a,b in ab:
  l[a].append(b)
  l[b].append(a)
  
r = [0]*(N+1)
i = 0
p = l[1]
q = deque()
flag = [False]*(N+1)
flag[1]=True
while (len(p)!=0)or(len(q)!=0):
  if i%2==0:
    while len(p)!=0:
      j = p.pop()
      if flag[j]:
        continue
      else:
        q.extend(l[j])
        flag[j]=True
        r[j]=1
    i+=1
  else:
    i+=1
    while len(q)!=0:
      j = q.pop()
      if flag[j]:
        continue
      else:
        p.extend(l[j])
        flag[j]=True
a = deque(range(1,N+1,3))
b = deque(range(2,N+1,3))
c = deque(range(3,N+1,3))
x = sum(r)
if x<=N//3:
  for i in range(1,N+1):
    if r[i]==1:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      else:
        ans[i-1]=b.pop()
elif (N-x)<=N//3:
  for i in range(1,N+1):
    if r[i]==0:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      else:
        ans[i-1]=b.pop()
else:
  for i in range(1,N+1):
    if r[i]==1:
      if len(a)!=0:
        ans[i-1]=a.pop()
      else:
        ans[i-1]=c.pop()
    else:
      if len(b)!=0:
        ans[i-1]=b.pop()
      else:
        ans[i-1]=c.pop()
        
print(' '.join(map(str,ans)))

Fixed submission:
N = int(input())
ab = [list(map(int,input().split())) for _ in range(N-1)]
from collections import deque
l = [deque() for _ in range(N+1)]
ans = [0]*N
for a,b in ab:
  l[a].append(b)
  l[b].append(a)
  
r = [0]*(N+1)
i = 0
p = l[1]
q = deque()
flag = [False]*(N+1)
flag[1]=True
while (len(p)!=0)or(len(q)!=0):
  if i%2==0:
    while len(p)!=0:
      j = p.pop()
      if flag[j]:
        continue
      else:
        q.extend(l[j])
        flag[j]=True
        r[j]=1
    i+=1
  else:
    while len(q)!=0:
      j = q.pop()
      if flag[j]:
        continue
      else:
        p.extend(l[j])
        flag[j]=True
    i+=1
a = deque(range(1,N+1,3))
b = deque(range(2,N+1,3))
c = deque(range(3,N+1,3))
x = sum(r)
if x<=N//3:
  for i in range(1,N+1):
    if r[i]==1:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(b)!=0:
        ans[i-1]=b.pop()
      else:
        ans[i-1]=c.pop()
elif (N-x)<=N//3:
  for i in range(1,N+1):
    if r[i]==0:
      ans[i-1]=c.pop()
    else:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(b)!=0:
        ans[i-1]=b.pop()
      else:
        ans[i-1]=c.pop()
else:
  for i in range(1,N+1):
    if r[i]==1:
      if len(a)!=0:
        ans[i-1]=a.pop()
      elif len(c)!=0:
        ans[i-1]=c.pop()
      else:
        ans[i-1]=b.pop()
    else:
      if len(b)!=0:
        ans[i-1]=b.pop()
      elif len(c)!=0:
        ans[i-1]=c.pop()
      else:
        ans[i-1]=a.pop()
        
print(' '.join(map(str,ans)))