For testing: Your problem is that you try to think of the result. Just don't fill it as you would fill in any other hanjie, by only filling in a square if you can explain why.. If you get stuck, change it a little near the area where you got trouble and retry.
Spoiler:
The number 18 inside a house, but it is not symmetrical.
For testing: Your problem is that you try to think of the result. Just don't fill it as you would fill in any other hanjie, by only filling in a square if you can explain why.. If you get stuck, change it a little near the area where you got trouble and retry.