Building Teams

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector <ll> vl;
typedef vector <vl> vvl;

bool dfs(const vvl &g, ll b, vl &team)
{
    for(auto x : g[b])
        if(team[x] == -1)
        {
            team[x] = 1 - team[b];
            if(!dfs(g, x, team))
                return false;;
        }
        else
            if(team[x] == team[b])
                return false;
            else;
    return true;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    ll n, m, a, b, i;
    cin >> n >> m;
    vvl g(n + 1);
    vl team(n + 1, -1);
    while(m--)
    {
        cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    for(i = 1; i <= n; i++)
    {
        if(team[i] == -1)
        {
            team[i] = 0;
            if(!dfs(g, i, team))
            {
                cout << "IMPOSSIBLE";
                return 0;
            }
        }
    }
    for(i = 1; i <= n; i++)
        cout << team[i] + 1 << " ";

    return 0;
}

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