A solution

[amichair]

Not sure why I did this thing in the first place :-) I suppose we all think about elevator algorithms while waiting for one.

I'd say half the challenge is distilling the actual requirements from the text, which is a bit verbose and not entirely clear about everything (and may or may not coincide with a real elevator, as opposed to the writer's assumptions) - or maybe it's just me. I wrote down the short list of actual logical rules I found in the text, but then had to update it with additional ones that were uncovered only by failing tests.

I suspect that if you'd give the well-defined list of rules up front (less than 10 lines) it would be a somewhat different experience. But perhaps that's part of the challenge... it did take longer than I expected, and I guess that's the point.

Anyway... here's a working solution.

[amichair]

btw it's nice to see the different kinds of solutions people came up with... can you post the original solution too? (perhaps in separate branch)

[mshang]

Nice! Thanks for your thoughts. I agree that the requirements could be more clearly communicated. I tried to only give the requirements inline with doctests that illustrated them. Maybe there needs to be a summary upfront like you say.

Others have submitted solutions in pull requests which I have closed, in order to keep the pull request tab clear for changes to the challenge itself. The first one was here: #2

[amichair]

I found the other solutions, though it took a while - perhaps you can link to them directly in the docs. And I was referring to your own solution that you can add to the bunch :-)