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input/code.cpp: In function 'void dfs(long long int)':
input/code.cpp:50:20: warning: statement has no effect [-Wunused-value]
   50 | #define debug(...) 42
      |                    ^~
input/code.cpp:66:13: note: in expansion of macro 'debug'
   66 |             debug(u, col[u], v, col[v]);
      |             ^~~~~

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

string to_string(string s) {
    return '"' + s + '"';
}
 
string to_string(const char* s) {
    return to_string((string) s);
}
 
string to_string(bool b) {
    return (b ? "true" : "false");
}
 
template <typename A, typename B>
string to_string(pair<A, B> p) {
    return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
 
template <typename A>
string to_string(A v) {
    bool first = true;
    string res = "{";
    for (const auto &x : v) {
        if (!first) {
            res += ", ";
        }
        first = false;
        res += to_string(x);
    }
    res += "}";
    return res;
}
 
void debug_out() {
    cerr << endl;
}
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << to_string(H);
    debug_out(T...);
}
 
#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

const int N = 2e5 + 5;

int n, m;
vector<int> adj[N];

int col[N];

void dfs(int u) {
    for (int v : adj[u]) {
        if (!col[v]) {
            col[v] = 3 - col[u];
            dfs(v);   
        } else {
            debug(u, col[u], v, col[v]);
            if (col[u] == col[v]) {
                cout << "IMPOSSIBLE\n";
                exit(0);
            }
        }
    }
}

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

    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }

    for (int i = 1; i <= n; i++) {
        if (!col[i]) {
            col[i] = 1;
            dfs(i);
        }
    }

    for (int i = 1; i <= n; i++) {
        cout << col[i] << ' ';
    }
}

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