Building Teams

import sys

#build adjacecny and get input
input_data = sys.stdin.read().split()#get whole input data at once
n_pupils = int(input_data[0])
n_friendships = int(input_data[1])

adj = [[] for _ in range(n_pupils+1)]

k = 2

for _ in range(n_friendships):
    a = int(input_data[k])
    b = int(input_data[k+1])
    adj[a].append(b)
    adj[b].append(a)
    k+=2


team = []
team1 = []
forbidden_from_team_1 = []
team2 = []
forbidden_from_team_2 = []
team.append(1) #add first student to a team
forbidden_from_team_1.extend(adj[1])

def solve():
        
    for i in range(2,n_pupils+1):
        if i in forbidden_from_team_1 and i in forbidden_from_team_2 :
            print("IMPOSSIBLE")
            return
        elif i in forbidden_from_team_1:
            team.append(2)
            forbidden_from_team_2.extend(adj[i])
        else :
            team.append(1)
            forbidden_from_team_1.extend(adj[i])

    print(*list(map(str,team)))
solve()

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED