Ruudukko

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

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n, m;
    cin >> n >> m;
    int z[n+1][n+1] {};
    for (int i = 0; i < m; ++i) {
        int y1, x1, y2, x2;
        cin >> y1 >> x1 >> y2 >> x2;
        y1--; x1--;
        z[y1][x1] ^= 1;
        z[y1][x2] ^= 1;
        z[y2][x1] ^= 1;
        z[y2][x2] ^= 1;
    }
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            if (i) z[i][j] ^= z[i-1][j];
            if (j) z[i][j] ^= z[i][j-1];
            if (i && j) z[i][j] ^= z[i-1][j-1];
            cout << (z[i][j] ? '#' : '.');
        }
        cout << "\n";
    }
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 2, 3

Verdict: ACCEPTED

Test 3

Group: 2, 3

Verdict: ACCEPTED

Test 4

Group: 3

Verdict: ACCEPTED

Test 5

Group: 3

Verdict: ACCEPTED