formatPrint function
Implementation
void formatPrint(List<int> arr) {
int element;
String out = "";
for (int index = 0; index < arr.length; ++index) {
element = arr[index];
if (index % 9 == 0) {
out += "\n";
if ((index ~/ 9) % 3 == 0 && index != 0) {
out += "\n";
}
}
out += '${element == -1 ? "." : element} ${(index + 1) % 3 == 0 ? "\t" : ""}';
}
print(out);
}