[DengSchoo]

I already want to write some codes to solve this perfect hard-level(LeetCode) algo problem.

[romes]

Let me know if you find some reasonably fast sub-optimal algorithm, I'd be interested in trying it.

There seems to be some literature on the complexity this kind of sliding puzzles, like https://www.sciencedirect.com/science/article/abs/pii/S03043....