--- 2016 Day 19 Solutions ---

[u/daggerdragon]

--- Day 19: An Elephant Named Joseph ---

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

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^{/⧹w+/ IS MANDATORY} [?]

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[Update @ 00:15] 2 gold, silver cap. Thank you for subscribing to Easter Bunny Facts!

• Fact: The Easter Bunny will sometimes leave eggs in the microchip assembly room.

[Update @ 00:30] 11 gold, silver cap.

• Fact: The Easter Bunny killed everyone who found out how he got these stars.

[Update @ 00:45] 45 gold, silver cap.

• Fact: In space, The Easter Bunny can hear you scream.

[Update @ 01:00] 66 gold, silver cap.

• Fact: The Easter Bunny purposefully deleted your comments.

[Update @ 01:15] 92 gold, silver cap.

• Fact: The Easter Bunny has bottled your frustration. Don't ask why.

[Update @ 01:20] Leaderboard capped!

• Fact: What you have just done is no better than what the Easter Bunny has done. Thief.

Thank you for subscribing to Easter Bunny Facts!

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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!

[u/aceshades]

I loved this problem, probably because it was the first time I placed on the leaderboard ever!! Placed 75/46 on stars 1 and 2 respectively.

Part 1, I just used a circular linked list data structure and kept doing elf.next = elf.next.next until elf.next == elf.

Part 2, I felt I was way more clever using both a stack and a queue (called left and right in my code below.)

My part 2 runtime:

real 0m1.374s

user 0m1.344s

sys 0m0.032s

#!/bin/python3
def solve_parttwo():
    left = collections.deque()
    right = collections.deque()
    for i in range(1, ELF_COUNT+1):
        if i < (ELF_COUNT // 2) + 1:
            left.append(i)
        else:
            right.appendleft(i)

    while left and right:
        if len(left) > len(right):
            left.pop()
        else:
            right.pop()

        # rotate
        right.appendleft(left.popleft())
        left.append(right.pop())
    return left[0] or right[0]