for (int i = 0; i <= n; i++) {
        for (int j = 0; j < A; j++) {
            cnt[i][j] += cnt[i - 1][j];
        }
    }

cnt[i][j] += cnt[i - 1][j]; in this line what happen when i=0; cnt[0][j]+=cnt[-1][j] as it has a index -1 does it make any sence

it is a editorial solution