Building Teams

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class BuildingTeams {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        int m = input.nextInt();
        boolean impossible = false;

        List<Integer> people = new ArrayList<>();
        List<Integer> friendless = new ArrayList<>();

        for (int i = 0; i < n; i++){
            friendless.add(i+1);
        }

        for (int i = 0; i < n; i++){
            people.add(1);
        }

        for (int j = 0; j < m; j++){
            int a = input.nextInt();
            int b = input.nextInt();

            int aTeam = people.get(a-1);
            int bTeam = people.get(b-1);
            if (aTeam == 1 && bTeam == 1){
                if (friendless.contains(a)){
                    people.set(a-1, 2);
                } else if(friendless.contains(b)){
                    people.set(b-1, 2);
                } else {
                    impossible = true;
                }
            }
            if (aTeam == 2 && bTeam == 2){
                impossible = true;
            }
            friendless.remove(Integer.valueOf(a));
            friendless.remove(Integer.valueOf(b));
        }
        if(impossible){
            System.out.println("IMPOSSIBLE");
        } else {
            people.forEach(team -> System.out.print(team + " "));
        }
    }
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: ACCEPTED

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: ACCEPTED

Test 6

Verdict: TIME LIMIT EXCEEDED

Test 7

Verdict: TIME LIMIT EXCEEDED

Test 8

Verdict: TIME LIMIT EXCEEDED

Test 9

Verdict: TIME LIMIT EXCEEDED

Test 10

Verdict: TIME LIMIT EXCEEDED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED