The challenge in question is this one, which is solving a couple 4x4 sliding puzzles (also known as 15 puzzle) with the least amount of moves in a certain time limit.

I posted an answer that computes optimal answers within the time limit, essentially ending the challenge. Such an answer is not possible in 5x5 puzzles and higher. And especially in large puzzles, e.g. 8x8 or 10x10 you need techniques that are approximations.

Since the challenge is 5+ years old, is essentially closed, and has an interesting extension into bigger sizes, would it be allowed to repost the challenge for those bigger sizes?

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    \$\begingroup\$ Any challenges that requires different tools to tackle on different scales are different challenges on different scales. I'd argue they are different enough to be their own levels, what matters is whether there is value in posting the redefined challenge, which is up to you to decide. \$\endgroup\$ – Unihedron Feb 14 '18 at 14:46

This should be allowed

4x4 puzzles have known optimal algorithms. Only rough bounds are known for 5x5, and only weak upper bounds are known up to 10x10. Including 5x5 and larger completely changes the challenge from "optimize the known optimal algorithm for time" to "come up with an algorithm that performs well in moves and time". I'd definitely consider those two to be different challenges.


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