

How wooden puzzles can destroy dev teams - johncs
http://engineering.khanacademy.org/posts/evil-puzzle.htm

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ChrisLomont
Interestingly, when I run this through an old Dancing Links [1] based solver I
wrote a while back for solving general puzzles, it solves the first one in
0.04 seconds, uses 65 columns, 242 rows, does 181510 de-queues, and finds a
unique solution.

The same solver on the hard version runs in 0.01 seconds, 67 columns, 272
rows, 245626 de-queues, and finds no solutions.

So as others have noted, the hard puzzle solution must be some weird rotation,
and/or not spaced on "integral" coordinates.

Since I don't have time to write such a solver, I will leave it for now :)

Note: if you have not looked at the Dancing Links paper by Knuth and learned
how to use it to solve backtracking problems, you should. It's amazingly
useful for solving such problems, for enumerating all solutions, and it is
fast and completely general.

[1] [http://arxiv.org/abs/cs/0011047](http://arxiv.org/abs/cs/0011047)

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shard
Assuming the solvers that they wrote searched the problem space correctly, the
hard side probably violates some assumption. My guess would be that on the
hard side the pieces can lock into some sort of 3D structure.

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throwaway_yy2Di
Maybe the rotation angles aren't simple multiples of 60°.

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mcphage
Or for that matter, the placement might not be at integral coordinates.

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fsk
What makes this a HARD puzzle is that the pieces don't completely fill the
area. That dramatically increases the solution search space.

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0x0
Any hints for the solution, then?

~~~
throwaway_yy2Di
Spoilers: [https://xkcd.com/356/](https://xkcd.com/356/)

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fredgrott
if they ever read Penrose it would have taken less time :)

