Building Teams

def function(n, graph):


    teams = [0] * n

    for i in range(n):
        if teams[i] == 0:
            queue = [i]
            teams[i] = 1
            head = 0
            while head < len(queue):
                u = queue[head]
                head += 1
                for v in graph[u]:
                    if teams[v] == 0:
                        teams[v] = 3 - teams[u]
                        queue.append(v)
                    elif teams[v] == teams[u]:
                        return []

    return teams

def main():
    n, m = map(int, input().split())
    friends = []

    for _ in range(m):
        a, b = map(int, input().split())

        friends.append([a, b])

    graph = [[] for _ in range(n)]
    for a, b in friends:
        graph[a-1].append(b-1)
        graph[b-1].append(a-1)


    results = function(n, graph)
    if results == []:
        print("IMPOSSIBLE")
        return
    for result in results:
        print(result, end=" ")



if __name__ == "__main__":
    main()

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED