So long as everything in the string can be contained in a single byte, this solution is fine. I'm trying to get into the habit of not assuming single bytes unless explicitly stated, though, so prefer the rune solution.

The ruby test cases are broken. The Cat catches the mouse despite the Dog being in between if the mouse is to the left of the Cat.

Collected from several runs...

Testing for "m..DC........" and 7
  ✘ It should work for random inputs too - Expected: "Caught!", instead got: "Protected!"

Testing for "mD......C..................." and 18
  ✘ It should work for random inputs too - Expected: "Caught!", instead got: "Protected!"

Testing for ".m.D........C................" and 11
  ✘ It should work for random inputs too - Expected: "Caught!", instead got: "Protected!"

It says $codons[Ruby] or some such. It's fairly confusing.

In Javascript, the preloaded hash is codons. I finally ended up putting it in myself rather than trying to figure out what it was called.

Looks good.

Needs random tests

Giacomo, one of the tests in the ruby version appears to be wrong (or www.timeanddate.com has a bug, which is certainly possible...)

You have

Test.assert_equals(unlucky_days(1001), 3, "should be: 3")

But http://www.timeanddate.com/calendar/?year=1001&country=1 shows the number of Friday the 13ths for 1001 to be 1 (which is also what I have).

The instructions are somewhat misleading: it isn't the nodes that are in-place, but the head pointers.

ROFL

As you no longer provide the working solution, you can mark this issue closed :)

another great one :)

The additional cases don't give the intermediate arrays, only the sums of (some of) them. (Some of them => the array can be transformed multiple times without those transformations being reported so long as the sum remains the same.) I need the intermediate arrays or some sort of context to figure out how to extract the pattern...