lessons/参考实现/07-二分图/CodeForces-741C.cpp

#include <iostream>
#include <queue>
#include <utility>
#include <vector>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n; cin >> n;
    vector<pair<int, int>> couple(n); vector<vector<int>> g(2 * n);
    for (auto &[a, b] : couple) {
        cin >> a >> b; --a; --b; g[a].push_back(b); g[b].push_back(a);
    }
    for (int i = 0; i < 2 * n; i += 2) {
        g[i].push_back(i + 1); g[i + 1].push_back(i);
    }
    vector<int> color(2 * n, -1);
    for (int s = 0; s < 2 * n; ++s) if (color[s] == -1) {
        queue<int> q; q.push(s); color[s] = 0;
        while (!q.empty()) {
            int u = q.front(); q.pop();
            for (int v : g[u]) {
                if (color[v] == -1) color[v] = color[u] ^ 1, q.push(v);
                else if (color[v] == color[u]) { cout << "-1\n"; return 0; }
            }
        }
    }
    for (auto [a, b] : couple) cout << color[a] + 1 << ' ' << color[b] + 1 << '\n';
}