I have some code for generating random boards, clues and then finding one solution for the board and have done some benchmarking:

6 x 6 takes average 76 ms to solve.
7 x 7 takes 670 ms to solve.
8 x 8 takes 14.95 seconds!

On, or after ?

Oh well, you'll have to do your own debugging anyway, bit hard to do from a distance .. good luck!

Ah! Thanks for the tip. It looks like my code is fast enough after all but is going into an infinite loop on the 4th "very hard" test.

Changed, thanks!

Clojure? ( Mention that next time! )

You're probably close. You might be in an infinite loop; there's a test at the end that sometimes throws people for a loop. Print inputs and intermediates!

Thanks for translating this, am enjoying the challenge.

I noticed a small error in the sample tests, both of the names are the same so the second test does not run.

Change the second skyscrapers-example-test1 -> skyscrapers-example-test2

My attempt completes four of the very hard tests but then times out. How many more tests are there, am I close to finishing?

Very succinct!

Nice. You could also use rest x here instread of subs x 1. Since you are using first pairing that with rest would seem better style.