Ruudukko

#include <iostream>
#include <cstdio>
using namespace std;
bool flip[2048][2048];
bool cur[2048];
int main() {
	int n,m;cin>>n>>m;
	while(m--){
		int y1,x1,y2,x2;
		cin>>y1>>x1>>y2>>x2;
		flip[y1][x1]^=1;
		flip[y1][x2+1]^=1;
		flip[y2+1][x1]^=1;
		flip[y2+1][x2+1]^=1;
	}
	for(int i=1; i<=n; ++i) {
		bool f=0;
		for(int j=1; j<=n; ++j) {
			f ^= flip[i][j];
			cur[j] ^= f;
			putchar(cur[j]?'#':'.');
		}
		putchar('\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