Problem p02749 (python)

Fixed submission:
import sys
input = sys.stdin.readline

def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))

import queue

def main():
    N=I()
    adj=[[] for _ in range(N)]
    mod1=range(1,N+1,3)
    n1=0
    mod2=range(2,N+1,3)
    n2=0
    mod12=list(mod1)+list(mod2)
    n12=0
    mod3=range(3,N+1,3)
    n3=0
    
    p=[0]*N
    
    for i in range(N-1):
        a,b=MI()
        a-=1
        b-=1
        adj[a].append(b)
        adj[b].append(a)
     
    
    q=queue.Queue()
    q.put((0,-1,0))#node,par,depth
    d=[0]*N#深さをメモ
            
        
    while not q.empty():
        v,par,depth=q.get()
        d[v]=depth%2
                
        for i in range(len(adj[v])):
            nxt=adj[v][i]
            if nxt!=par:
                q.put((nxt,v,depth+1))
                
    dmod=[0,0]
    for i in range(N):
        dmod[d[i]]+=1
        
    if dmod[0]<=(N//3):
        for i in range(N):
            if d[i]==0:
                p[i]=mod3[n3]
                n3+=1
            else:
                if n12<len(mod12):
                    p[i]=mod12[n12]
                    n12+=1
                else:
                    p[i]=mod3[n3]
                    n3+=1
    elif dmod[1]<=(N//3):
        for i in range(N):
            if d[i]==1:
                p[i]=mod3[n3]
                n3+=1
            else:
                if n12<len(mod12):
                    p[i]=mod12[n12]
                    n12+=1
                else:
                    p[i]=mod3[n3]
                    n3+=1         
    
    else:
        for i in range(N):
            if d[i]==1:
                if n1<len(mod1):
                    p[i]=mod1[n1]
                    n1+=1
                else:
                    p[i]=mod3[n3]
                    n3+=1
            else:
                if n2<len(mod2):
                    p[i]=mod2[n2]
                    n2+=1
                else:
                    p[i]=mod3[n3]
                    n3+=1     
    
                
    print(' '.join(map(str, p)))
        
        
    
    
        
                
            
        
        
    

main()

Buggy submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline

def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))

import queue

def main():
    N=I()
    adj=[[] for _ in range(N)]
    mod1=range(1,N+1,3)
    n1=0
    mod2=range(2,N+1,3)
    n2=0
    mod3=range(3,N+1,3)
    n3=0
    
    p=[0]*N
    
    for i in range(N-1):
        a,b=MI()
        a-=1
        b-=1
        adj[a].append(b)
        adj[b].append(a)
     
    
    q=queue.Queue()
    q.put((0,-1,0))#node,par,depth
    d=[0]*N#深さをメモ
            
        
    while not q.empty():
        v,par,depth=q.get()
        d[v]=depth%2
                
        for i in range(len(adj[v])):
            nxt=adj[v][i]
            if nxt!=par:
                q.put((nxt,v,depth+1))
                
    dmod=[0,0]
    for i in range(N):
        dmod[d[i]]+=1
        
    for i in range(N):
        bit=d[i]
        if dmod[bit]<dmod[(bit+1)%2]:
            if n3<len(mod3):
                p[i]=mod3[n3]
                n3+=1
            elif bit==1:
                if n1<len(mod1):
                    p[i]=mod1[n1]
                    n1+=1
                else:
                    p[i]=mod2[n2]
                    n2+=1
            else:
                if n2<len(mod2):
                    p[i]=mod2[n2]
                    n2+=1
                else:
                    p[i]=mod1[n1]
                    n1+=1
                
        else:
            if bit==1:
                if n1<len(mod1):
                    p[i]=mod1[n1]
                    n1+=1
                else:
                    p[i]=mod2[n2]
                    n2+=1
            else:
                if n2<len(mod2):
                    p[i]=mod2[n2]
                    n2+=1
                else:
                    p[i]=mod1[n1]
                    n1+=1
            
        
                    
                
    
                
    print(' '.join(map(str, p)))
        
        
    
    
        
                
            
        
        
    

main()