18
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Samantha had been fiddling with something at her desk for ages, and constantly scribbling notes on a piece of paper. When my curiosity eventually got the better of me, I wandered over to ask what she was up to.

"No, no!" she exclaimed. "Don't look yet! I'm still on the simple version. Once I work out how to solve the more difficult version, then I'll show you the puzzle. Just give me another few minutes."

"But what's it all about?"

"Oh all right, you can look at this." She handed me a sheet of paper with two sequences of numbers written on it. "That's the solution to one case of the simple version. You won't be able to deduce anything from it though, not until I tell you what it's all about."

I looked at the paper in my hand. It read as follows:

(6 4 8 7 5 3 1 2)

3 5 2 1 7 6 4 2 1 3 5 8 2 1 3 5 8 3 6 4 1 2 3 6 5 8

"Challenge accepted!" I said.

But damn, I can't actually figure out what kind of puzzle Samantha is studying. Can you help?

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  • 1
    $\begingroup$ Probably unnecessary disclaimer: this isn't a true story, and in fact I do know what the solution is. $\endgroup$ – Rand al'Thor Sep 21 '16 at 14:15
  • 1
    $\begingroup$ "That's the solution to one case". Does this mean that there are/may be more solutions and all of them consist of 26 numbers? $\endgroup$ – Marius Sep 21 '16 at 14:19
27
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It's a...

sliding block puzzle!

The board is originally in the state

given by the numbers in the parentheses: top row 648, middle row 753, bottom row 12(blank).

The sequence of numbers

gives the order in which to slide the tiles into the empty space.

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  • 1
    $\begingroup$ You my sir, are a genius. $\endgroup$ – The Great Duck Sep 22 '16 at 4:20
  • $\begingroup$ Now here is a second challenge: find a better solution to the original puzzle without using the original board. $\endgroup$ – The Great Duck Sep 22 '16 at 4:20
  • $\begingroup$ @TheGreatDuck: I don't understand what you mean. A "better solution"? But it's a different puzzle if the original board is different. $\endgroup$ – Deusovi Sep 22 '16 at 4:23
  • $\begingroup$ I mean find a way to somehow simplify the motions in the solution without looking at WHAT the original board looked like. I.E. simplify the operations 'blindly'. $\endgroup$ – The Great Duck Sep 22 '16 at 4:29
  • $\begingroup$ @TheGreatDuck The process for doing so would generate the original board midway through; I'm not sure it would be possible to find a simpler path without resetting to the origin state unless there are loops in the given path. $\endgroup$ – Passage Oct 27 '16 at 15:05

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