Shared code

#include <bits/stdc++.h>
using namespace std;

vector<int> TwoColor(vector<vector<int>>& graph) {
    int n = graph.size();
    vector<int> col(n, -1);
    queue<int> q;
    for (int i = 0; i < n; i++) {
        if (col[i] == -1) q.push(i), col[i] = 0;
        while (q.size()) {
            int u = q.front(); q.pop();
            for (auto v : graph[u]) {
                if (col[v] == col[u]) return {};
                if (col[v] == -1) {
                    col[v] = col[u]^1; // sets color to opposite of current
                    q.push(v);
                }
            }
        }
    }
    return col;
}

int main() {
    cin.tie(0)->sync_with_stdio(0);

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

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

    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        u--; v--;
        graph[u].push_back(v);
        graph[v].push_back(u);
    }

    vector<int> col = TwoColor(graph);

    if (col.empty()) cout << "IMPOSSIBLE\n";
    else for (auto v : col) cout << v+1 << ' ';
    return 0;
}