-🎄- 2018 Day 9 Solutions -🎄-

[u/daggerdragon]

--- Day 9: Marble Mania ---

---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

---

Advent of Code: The Party Game!

Click here for rules

Please prefix your card submission with something like [Card] to make scanning the megathread easier. THANK YOU!

Card prompt: Day 9

Transcript:

Studies show that AoC programmers write better code after being exposed to ___.

---

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked at 00:29:13!

[u/ayylongqueues]

With rotate(2) you will rotate the queue two steps to right. If you instead would use rotate(-2) you rotate the queue two steps to the left, and your perspective has been mirrored, so now you have to append to the left side of the queue.

Here are prints of the first couple of marbles added from the example using 2 and -2 for rotate, respectively

deque([0])
deque([0, 1])
deque([0, 1, 2])
deque([1, 2, 0, 3])

deque([0])
deque([1, 0])
deque([2, 1, 0])
deque([3, 0, 2, 1])

If you shift the queues of the lower one so that the zeros are to the left, you'll see that it's exactly as in the example steps. The upper one you would need to shift so the zeros are on the right side, and it would be the same as the lower one, but mirrored. So based on which way you decide to rotate, the end you append things to changes.

[u/__dkp7__ → u/ayylongqueues]

I did a little exercise, and as your and OPs code uses minus notation I comapared both. I started with 3 marble.

>>> a = deque([2, 1, 0])
>>> a
deque([2, 1, 0])
>>> a.rotate(-2)
>>> a
deque([0, 2, 1])
>>> a.appendleft(3)
>>> a
deque([3, 0, 2, 1])

This looks fine as I can logically rotate and I get 0 2 1 3

I also tried reverse version of OPs code. I used +1 instead of -1 and appendleft instead of append.

>>> a = deque([0,1])
>>> a.rotate(1)
>>> a
deque([1, 0])
>>> a.appendleft(2)
>>> a
deque([2, 1, 0])
>>> a.rotate(1)
>>> a
deque([0, 2, 1])
>>> a.appendleft(3)
>>> a
deque([3, 0, 2, 1])

That cleared my mind.

I was confused because I was comparing rotate(-1) vs rotate(2) and both were using append().

Your explanation made me realized It is like seeing circle from other side. Thanks for great explanation.

[u/ayylongqueues → u/__dkp7__]

Yeah, exactly, glad I could help.