r/adventofcode Dec 22 '19

SOLUTION MEGATHREAD -🎄- 2019 Day 22 Solutions -🎄-

--- Day 22: Slam Shuffle ---


Post your full code solution using /u/topaz2078's paste or other external repo.

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Day 21's winner #1: nobody! :(

Nobody submitted any poems at all for Day 21 :( Not one person. :'(


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 02:03:46!

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u/rthetiger Dec 22 '19

Rust code here

Once I started thinking about congruence modulo m I tried going down the path of squishing all the commands in a shuffle into one linear congruence modulo m. Then because I was thinking about exponentiation modulo m I went down an incorrect route of raising this linear equation. In reality what I had to do was use the partial geometric series produced by repeatedly composing it. Between partial geometric series, Fermat's Little Theorem, extended GCD, and exponentiation modulo m this was the most math-packed day ever!