Building Teams

def main():
    pupils, frienships = [int(x) for x in input().split()]
    adj_list = {k:[] for k in range(1, pupils+1)}
    groups = [0 for _ in range(pupils+1)]
    stack = []
    previous = 2

    for _ in range(frienships):
        pupil1,pupil2 = [int(x) for x in input().split()]
        adj_list[pupil1].append(pupil2)
        adj_list[pupil1].append(pupil1) 



    for pupil in adj_list:
        if groups[pupil] == 0:
            if previous==1:
                previous=2
            else:
                previous=1

            stack.append(pupil)
            groups[pupil] = previous 

            while stack:
                aux = stack.pop()
                for x in adj_list[aux]:
                    if groups[x] == 0:
                        stack.append(x)
                        groups[x] = 1 if previous == 2 else 2

        elif groups[pupil] == previous:
            print("IMPOSSIBLE")
            return
            
    salida = ""
    for x in range(1, pupils+1):
        salida+=str(groups[x]) + " "
    print(salida[:-1])             


main()

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: WRONG ANSWER

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: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER