15 Puzzle - Collect numbers

I present to your attention the classic version of the game 15 Puzzle. Exactly the way Noyes Chapman came up with it in 1874. I only added difficulty levels and an auto build feature. The assembly function is intended, first of all, to check the collectibility of the required combination of numbers, if you suddenly have doubts. There are no uncollectible combinations in my game. I would be grateful for donations that stimulate my creativity.