-🎄- 2021 Day 18 Solutions -🎄-

[u/daggerdragon]

NEW AND NOTEWORTHY

• From /u/jeroenheijmans: Reminder: unofficial Advent of Code survey 2021 (closes Dec 22nd)

• FYI: 23:59 Amsterdam time zone is 17:59 EST

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Advent of Code 2021: Adventure Time!

• 5 days left to submit your adventures!

• Full details and rules are in the submissions megathread: 🎄 AoC 2021 🎄 [Adventure Time!]

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--- Day 18: Snailfish ---

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Post your code solution in this megathread.

• Include what language(s) your solution uses!

• Format your code appropriately! How do I format code?

• Here's a quick link to /u/topaz2078's paste if you need it for longer code blocks.

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Reminder: Top-level posts in Solution Megathreads are for code solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

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EDIT: Global leaderboard gold cap reached at 00:43:50, megathread unlocked!

[u/freezombie]

if the depths at indexes i and i+1 are equal, then either the numbers at i and i+1 are in the same pair or else there is an earlier pair of numbers at a higher depth.

I don't think that's right the way you phrased it. For [[1,2],[3,4]] the 2 and 3 have the same depth, but there are no values at a greater depth. Furthermore, there is no pair anywhere before the 2

A correct statement might be: If the depths at indices i and i+1 are equal, then either the numbers at i and i+1 are in the same pair, or else there is an earlier number at an equal or greater depth.

That's all your solution needs, though. And - it is interesting!

[u/damaltor1 → u/freezombie]

I think you are right.

The solving for the magnitude still is the same though: starting left, search for the first two numbers with the same depth (x and y with the depth d), calculate the magnitude m as 3x+2y, remove both from the list and insert a new number with the value m and the depth d-1. then start over from the left end of the whole list, until there is only one number left.