Connected Component, 2-SAT

#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
typedef long long LL;
typedef pair<int, int> P;
typedef double ld;
const double EPS = 1e-9;
const double PI = acos(-1.0);
const int N = 1e5 + 10;
const int INF = 1e9 + 7;
const int MOD = 1e9 + 7;
/********** head **********/

int n, m;
vector<int> G[N], rG[N], vs;
int used[N], cmp[N];

void add_edge(int from, int to) {
    G[from].push_back(to);
    rG[to].push_back(from);
}

void dfs(int v) {
    used[v] = true;
    for (int u: G[v]) {
        if (!used[u])
            dfs(u);
    }
    vs.push_back(v);
}

void rdfs(int v, int k) {
    used[v] = true;
    cmp[v] = k;
    for (int u: rG[v])
        if (!used[u])
            rdfs(u, k);
}

int scc() {
    memset(used, 0, sizeof(used));
    vs.clear();
    for (int v = 0; v < n; ++v)
        if (!used[v]) dfs(v);
    memset(used, 0, sizeof(used));
    int k = 0;
    for (int i = (int) vs.size() - 1; i >= 0; --i)
        if (!used[vs[i]]) rdfs(vs[i], k++);
    return k;
}

int main() {
    cin >> n >> m;
    n *= 2;
    for (int i = 0; i < m; ++i) {
        int a, b; cin >> a >> b;
        add_edge(a - 1, (b - 1) ^ 1);
        add_edge(b - 1, (a - 1) ^ 1);
    }
    scc();
    for (int i = 0; i < n; i += 2) {
        if (cmp[i] == cmp[i + 1]) {
            puts("NIE");
            return 0;
        }
    }
    for (int i = 0; i < n; i += 2) {
        if (cmp[i] > cmp[i + 1]) printf("%d\n", i + 1);
        else printf("%d\n", i + 2);
    }
}