Awesome. Special thanx for 5x5 mode

30 minutes later I understand that I got unsolvable combination :-)

I was about to ask you this, haha. How long took you to notice?

I read a guide on how to solve 8-puzzle, and even with the guide I couldn't solve it. So I went to the math of it, and read an article[1] that gives a proof if a board is solvable or not.

Dumb me! The way I was creating the board I would make it unsolvable with a even board (4x4). The 3x3 and 5x5 were fine.

The bug is fixed. Sorry about that. I'm laughing so hard because even I couldn't solve any 4x4 games.

1 - https://www.geeksforgeeks.org/check-instance-15-puzzle-solva...

I solved all of them except last 2 pieces, next 15-20 minutes made me sure that something has gone wrong. I decided to read more about these puzzles and knew that they're unsolvable in 50% cases.

That was funny, thanks a lot!