1864D - Matrix Cascade - CodeForces Solution

#include <cstdio>
#include <algorithm>
#include <vector>
#include <set>
#include <queue>
#include <cmath>
#include <cstdlib>
#include <utility>
#include <cstring>

using namespace std;

#define ll long long
#define MOD // Insert modulo here
#define mul(a, b) (((ll)(a) * (ll)(b)) % MOD)

#ifndef ONLINE_JUDGE
#define debug(format, ...) fprintf(stderr, \
    "%s:%d: " format "\n", __func__, __LINE__,##__VA_ARGS__)
#else
#define debug(format, ...)
#define NDEBUG
#endif
bool grid[3005][3005];
char tmp[3005];
bool flag1[3005][3005];
bool flag2[3005][3005];
void work()
{
    int n;
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        scanf("%s", tmp + 1);
        for (int j = 1; j <= n; j++) {
            grid[i][j] = (tmp[j] == '1');
        }
    }
    int ans = 0;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            if (flag1[i][j]) {
                grid[i][j] = !grid[i][j];
                if (j == 1) {
                    flag1[i+1][j] = !flag1[i+1][j];
                    flag2[i+1][j+1] = !flag2[i+1][j+1];
                } else {
                    flag1[i+1][j-1] = !flag1[i+1][j-1];
                    flag2[i+1][j] = !flag2[i+1][j];
                    flag2[i+1][j+1] = !flag2[i+1][j+1];
                }
            }
            if (flag2[i][j]) {
                grid[i][j] = !grid[i][j];
                flag2[i+1][j+1] = !flag2[i+1][j+1];
            }
            if (grid[i][j]) {
                ans++;
                if (j == 1) {
                    flag1[i+1][j] = !flag1[i+1][j];
                    flag2[i+1][j+1] = !flag2[i+1][j+1];
                } else {
                    flag1[i+1][j-1] = !flag1[i+1][j-1];
                    flag2[i+1][j] = !flag2[i+1][j];
                    flag2[i+1][j+1] = !flag2[i+1][j+1];
                }
            }
        }
    }
    printf("%d\n", ans);
    for (int i = 0; i <= n + 3; i++) {
        for (int j = 0; j <= n + 3; j++) {
            grid[i][j] = flag1[i][j] = flag2[i][j] = false;
        }
    }
}
int main()
{
    int t; scanf("%d", &t);
    for (int i = 1; i <= t; i++) work();
    return 0;
}