Ruudukko

#include <iostream>
#include <string>
using namespace std;

bool M[2048][2048];

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