Kata

This same kata was mentioned earlier in a different comment.

I'll repeat what I mentioned there:

Although I may be biased, I would still argue that this kata is considerably different given the rules and data structure. E.g. there's an arbitrarily large range of floors to handle, basements are allowed, the elevator stops in less places, etc. I would imagine solutions would need to be quite different.

These are completely different algorithms that just both happened to involve elevators.

Okey, I was finally able to solve it. :D These were the test cases that helped me debug and find the problem:

puzzle = [{'from': 39, 'to': 14}, {'from': 6, 'to': 0}, {'from': 10, 'to': 6}, {'from': 8, 'to': 43}, {'from': 20, 'to': 2}, {'from': 7, 'to': 32}, {'from': 41, 'to': 37}, {'from': 37, 'to': 21}, {'from': 19, 'to': -1}, {'from': 21, 'to': 4}, {'from': 1, 'to': 23}, {'from': 34, 'to': -3}, {'from': 19, 'to': -3}, {'from': 9, 'to': 39}, {'from': 0, 'to': 26}, {'from': 26, 'to': 18}, {'from': 36, 'to': 18}, {'from': 6, 'to': 33}] solution = [39, 37, 36, 34, 26, 21, 18, 14, 10, 6, 4, 0, -3, 0, 1, 6, 7, 8, 23, 26, 32, 33, 43, 41, 37, 20, 19, 2, -1, -3, 9, 39] tester(29, puzzle, solution) puzzle = [{'from': 4, 'to': 20}, {'from': 12, 'to': 2}, {'from': 22, 'to': 24}, {'from': 9, 'to': 39}, {'from': 30, 'to': 45}, {'from': 5, 'to': 26}, {'from': -3, 'to': 43}, {'from': 36, 'to': 25}, {'from': 10, 'to': 13}, {'from': 42, 'to': 24}, {'from': 25, 'to': 28}, {'from': 39, 'to': 6}, {'from': 4, 'to': 3}, {'from': 7, 'to': 9}, {'from': 33, 'to': 0}, {'from': 24, 'to': 10}, {'from': 2, 'to': 41}, {'from': 36, 'to': 38}, {'from': 16, 'to': 27}, {'from': 12, 'to': 19}, {'from': 24, 'to': 31}, {'from': 14, 'to': 42}, {'from': 30, 'to': 34}, {'from': 33, 'to': 0}, {'from': 0, 'to': 10}, {'from': 4, 'to': 32}, {'from': 2, 'to': 16}, {'from': -1, 'to': 14}, {'from': 24, 'to': 8}, {'from': 14, 'to': 3}, {'from': 39, 'to': -3}, {'from': 8, 'to': 45}, {'from': 36, 'to': -1}, {'from': 3, 'to': -2}, {'from': 42, 'to': 30}, {'from': 7, 'to': 39}, {'from': 11, 'to': -3}, {'from': 45, 'to': 13}, {'from': 33, 'to': 28}, {'from': 24, 'to': 19}, {'from': 38, 'to': 41}, {'from': 32, 'to': 34}, {'from': 24, 'to': 40}, {'from': 16, 'to': 34}, {'from': 22, 'to': 39}, {'from': 30, 'to': 39}, {'from': 45, 'to': 4}, {'from': 25, 'to': 0}, {'from': 11, 'to': 8}, {'from': 37, 'to': 36}, {'from': 45, 'to': -2}, {'from': 38, 'to': 6}, {'from': 18, 'to': 1}, {'from': -2, 'to': 22}] solution = [4, 5, 7, 9, 20, 22, 24, 26, 30, 31, 32, 34, 36, 38, 39, 41, 45, 42, 30, 25, 24, 13, 12, 10, 4, 3, 2, 0, -2, -3, -2, -1, 0, 2, 10, 13, 14, 16, 22, 27, 30, 34, 39, 41, 42, 43, 39, 38, 37, 36, 25, 24, 8, 6, -1, -3, 2, 8, 12, 16, 19, 24, 25, 28, 30, 34, 39, 40, 45, 33, 28, 24, 19, 18, 14, 11, 3, 1, 0, -3, 11, 8] tester(7, puzzle, solution)

Yep, very good, thanks. My solution fails only 2 tests now, one of them being Day 14 (exactly this one you've pointed out) from the sample tests, so very easy to debug it. :)

Yes, now you have a really challenging kata.

Hmm, these 3 rules are supposed to explain that situation:

People on each floor get on you in the order they are queued as long as you're stopped on their floor. They always enter or leave you one at a time.

During a stop, all passengers who can get off gets off before any new passengers could get on.

When you're empty and you're on the same floor as the next person in the queue, you must now go in the direction they want to go.

Maybe I can better emphasize "enter or leave" as being one or the other but not both at the same time. The second rule is meant to apply anytime you're empty including during a stop, which would therefore imply a possible change in direction.

Yes, the enter or leave part is crucial in this case. It's the only edge case I found that could be interpreted ambiguously (imo).

Okay, I updated the rules to be clearer (hopefully)!

The elevator won't stop due to:

You must stop at each floor you pass that you can drop off and/or pick up passengers. Conversely, you don't stop if you're not changing passengers.

When the elevator reaches floor 85 and no one is getting off and the elevator is too full to hold any more, then there will be no change of passengers.

It is quite possible for the first person queued to be the last passenger of the day/run according to the rules. There should be such an example in the test cases in fact.

Cool, thanks. I thought it may be an exception because in this case 85 was the exact destination of the elevator.

What a disappointing answer :/ You haven't answered a thing. I'm not even going to bother raising an issue about missing and conflicting specs. I'm done here.

I was trying to give you a hint. The rule you cited was referring to when you're holding passengers. I pointed out the 2 rules that can force you to change directions. Also, sorry, I was still planning to give the answer as a spoiler comment.

The answer for the first one ([ { from: 4, to: 2}, { from 5, to: 4 } ]) is as you described it in your second bullet:

• Since you're empty, you move toward floor 4 where the first person is. (traveling UP)
• You reach floor 4 still empty, so you're forced to switch directions. They want to go down, so your direction is now DOWN.
• Incidentally, they see you go down, which is where they want to go. You pick up the first person on floor 4. (First stop)
• You now go to 2 to drop them off. (Second stop)
• Without further impedence, you go to 5 to pick up the next person (third stop).
• You drop them off at 4 (fourth stop).

[4, 2, 5, 2]

Hopefully, I illustrated that well. For [ { from: 4, to: 2}, { from 2, to: 5 } ], it would be as you described it in your first bullet. Your stops would be [2, 5, 4, 2]. I.e. you pick the person traveling in your direction, which then forces you to continue traveling past the first in queue since you're now holding passengers and can't switch directions.

I hope that's clear, and I'm sorry for upsetting you.

Marking the comment as a spoiler is not helpful for people who didn't solve the kata.

Oh okay, I think I'm starting to get it. I thought of it as a hint that you had to confirm to see, but now I realize that you have to unlock all solutions just to see one spoiler. Thanks for pointing that out!

I think the comment is more reasonable to show in that case so I unmarked it then.

Ok it makes sense now. I was able to pass the kata, but my solution doesn't fully synchronise with the ref sol. I need to investigate which solution is not entirely correct. It was a bit surprising when people get out of the elevator, and it becomes empty, that other people on the same floor that want to take the elevator have to wait, if the next person in queue is not on this floor. I'm sure these people would curse.

EDIT: new solution added, in sync with ref sol. There was 1 edge case I didn't take into account. I added a comment on the top to check if this edge case is explained in the rules (well enough).

Yes, sorry about the confusion.

It was a bit surprising when people get out of the elevator, and it becomes empty, that other people on the same floor that want to take the elevator have to wait, if the next person in queue is not on this floor. I'm sure these people would curse.

Although I took some creative liberties here, I tried to model it around how I found some elevators to work. But mainly, I started from the perspective of the elevator and I had a vague idea of respecting the order of when UP or DOWN buttons across all floors are pushed. Also since many elevators indicate its next direction on arrival, I continued with the idea that it ALWAYS indicates its direction as long as there was somewhere it knew it should go to. That's roughly how the rules here ended up forming.

Actually, I noticed people that can still hop on to the floor of the next person in queue, are allowed so. So it is a fair system nonetheless.

If you can't pick someone because you're full then you have no reason to stop.
If the elevator is full, you can only go unload someone.

I'd say it's different enough, there are more than a few differents rules.

When I was searching for similar katas, I never found this. I'll have to try it :)

Although I may be biased, I would still argue that this kata is considerably different given the rules and data structure. E.g. there's an arbitrarily large range of floors to handle, basements are allowed, the elevator stops in less places, etc. I would imagine solutions would need to be quite different.

I agree, if we allow different kata's for different type of sorting algorithms, we should also about different type of elevator algorithms.

I actually thought it would be expected and physical, hence why I added it. Some buildings have floors below 1 or negative floors, although they are typically thought of as basements.

I figured more people would find it odd if negative numbers weren't tested so I'm not sure how to respond to your comment.

I figured more people would find it odd if negative numbers weren't tested

Yes, but it was never specified either, and whether floors are non-negative or not (as well as how high floors can go) will affect implementation approaches.

So at least the floor range should be specified.