Building Teams

#include "bits/stdc++.h"

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;

#define F first
#define S second
#define PB push_back
#define MP make_pair

#define REP(i,a,b) for (int i = a; i < b; i++)

bool visit(int v, vector<bool> &visited, const vector<vector<int>> &edges, vector<bool> &belongsA, bool prev) {
    if(visited[v]) {
        if(belongsA[v] && prev) {
            return false;
        } else {
            return true;
        }
    }
    visited[v] = true;
    if(prev)  {
        belongsA[v] = false;
    } else {
        belongsA[v] = true;
    }

    bool can = true;
    for(auto e: edges[v]) {
        can = can && visit(e, visited, edges, belongsA, belongsA[v]);
    }
    return can;
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    int n, m;
    cin >> n >> m;

    vector<vector<int>> edges(n);

    REP(i, 0, m) {
        int a, b;
        cin >> a >> b;
        edges[a-1].PB(b-1);
        edges[b-1].PB(a-1);
    }

    vector<bool> visited(n);
    vector<bool> belongsA(n);

    int idx = 0;
    bool can = true;
    while(idx < n) {
        can = can & visit(idx, visited, edges, belongsA, false);
        while(idx < n && visited[idx]) {
            idx++;
        }
    }
    
    if(!can) {
        cout << "IMPOSSIBLE" << "\n";
    } else {
        REP(i, 0, n) {
            int val;
            val = belongsA[i] ? 1 : 2;
            cout << val << " ";
        }
        cout << "\n";
    }

    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: WRONG ANSWER