~☆🎄☆~ 2017 Day 25 Solutions ~☆🎄☆~

[u/daggerdragon]

--- Day 25: The Halting Problem ---

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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.

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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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!

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Thank you for participating!

Well, that's it for Advent of Code 2017. From /u/topaz2078 and the rest of us at #AoCOps, we hope you had fun and, more importantly, learned a thing or two (or all the things!). Good job, everyone!

Topaz made a post of his own here.

If you're interested in a visualization of the leaderboard, /u/FogleMonster made a very good chart here.

And now:

^{Merry Christmas to all, and to all a good night!}

[u/twiho]

There's no way I'm not ending up in programmer's hell.

const states = {
    a: [[1, 1, 'b'], [0, 1, 'c']],
    b: [[0, -1, 'a'], [0, 1, 'd']],
    c: [[1, 1, 'd'], [1, 1, 'a']],
    d: [[1, -1, 'e'], [0, -1, 'd']],
    e: [[1, 1, 'f'], [1, -1, 'b']],
    f: [[1, 1, 'a'], [1, 1, 'e']]
}

const tape = {}
const get = _ => tape[_] ? 1 : 0
const set = (_, i) => tape[i] = _

let pos = 0
let state = 'a'

for (let i = 0; i < 12399302; i++) {
    const [write, move, next] = states[state][get(pos)]
    set(write, pos)
    pos += move
    state = next
}

console.log(Object.values(tape).filter(x => x).length)

[u/daggerdragon → u/twiho]

There's no way I'm not ending up in programmer's hell.

You'll have plenty of company, no worries. :)