Dead Drop Gorgeous - BIO 2022 Round 2

#include <bits/stdc++.h>

using namespace std;

int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    int n; cin >> n;
    vector<int> g[2][2]; // bipartate graph between rows and columns
    /* g[i][j][k] specifies edges in the following way:
     i = 0 when the edge is from row to column and 1 when vice versa
     j = 0 when edge is an alpha and 1 when edge is a beta
     k = the index of the col/row connected to this row/col by this edge
    */
    for (int i = 0; i < 2; ++i) {
        for (int j = 0; j < 2; ++j) g[i][j].resize(n);
    }
    for (int i = 0; i < n; ++i) {
        int x, y; cin >> x >> y;
        g[1][0][x] = y;
        g[0][0][y] = x;
    }
    for (int i = 0; i < n; ++i) {
        int x, y; cin >> x >> y;
        g[1][1][x] = y;
        g[0][1][y] = x;
    }

    vector<int> p[2];
    p[0].resize(n), p[1].resize(n);
    for (int i = 0; i < n; ++i) p[0][i] = p[1][i] = i;

    vector<bool> seenRow(n);
    for (int i = 0; i < n; ++i) {
        if (seenRow[i]) continue;
        int a = i, b = i, side = 0; // side = 0 when on rows and 1 when on columns
        do {
            if (side == 0) seenRow[a] = seenRow[b] = true;
            swap(p[side][a], p[side][b]);
            a = g[side][1][a];
            b = g[side][0][b];
            swap(a, b);
            side = 1-side;
        } while (a != b);
        seenRow[a] = seenRow[b] = true;
    }

    for (int &x : p[0]) cout << x << ' ';
    cout << endl;
    for (int &x : p[1]) cout << x << ' ';
    cout << endl;
    return 0;
}