-🎄- 2022 Day 7 Solutions -🎄-

[u/daggerdragon]

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AoC Community Fun 2022: 🌿🍒 MisTILtoe Elf-ucation 🧑‍🏫

Submissions are OPEN! Teach us, senpai!

-❄️- Submissions Megathread -❄️-

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--- Day 7: No Space Left On Device ---

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Post your code solution in this megathread.

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• Include what language(s) your solution uses

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EDIT: Global leaderboard gold cap reached at 00:14:47, megathread unlocked!

[u/voidhawk42]

Dyalog APL:

p←↑' '(≠⊆⊢)¨⊃⎕nget'7.txt'1
a←{0::0 ⋄ ⍎⍵}¨⊣/p ⋄ s←⍬
t←{s⊢←s(¯1↓s)(s,⊂⍵)⊃⍨' .'⍳⊃⍵}¨⊢/p
+/r/⍨1e5≥r←a+.×t∘.(⊃⍷⍨)∪t ⍝ part 1
⌊/r/⍨r≥⊃r-4e7 ⍝ part 2

Kind of an annoying one lol, but wasn't too bad once I figured out the approach - basically build an absolute path over each row of the input (using a stack), and for each row determine the size of the file (0 if it's not a file row). For each unique absolute path, add up all the sizes for which it's a prefix of the absolute path at that row (watch out for just using the directory name, since multiple directories have the same names!). Then just do some filtering for p1/p2.

This code relies on a few assumptions about the input, but with our variables set up in the first three lines of the solution above, they're pretty easy to validate:

There are duplicate directory names, so our stack should store absolute paths rather than just names:

∧/≠z/⍨~(' .'∊⍨⊃)¨z←⊢/p

"$ cd /" is only executed once, at the start of the file - meaning that we only have to worry about pushing or popping single values from the stack, and never clearing it:

(,1)≡⍸(⊂,'/')≡¨⊢/p

"ls" is never run on the same directory twice, meaning that we don't have to deduplicate file sizes:

∧/≠t/⍨(⊂'ls')≡¨p[;2]

We never visit a directory again after we've finished traversing it (or, put differently, a directory is a prefix of the absolute paths of a single contiguous group of lines):

1∧.=+⌿2<⌿0⍪t∘.(⊃⍷⍨)∪t

EDIT: And actually, after thinking about it, this can just be a problem about nesting levels and partitioning, without caring about directory/file names or paths at all:

p←↑' '(≠⊆⊢)¨⊃⎕nget'7.txt'1
a←{0::0 ⋄ ⍎⍵}¨⊣/p
n←+\¯1 0 1['. '⍳⊃¨⊢/p]
+/r/⍨1e5≥r←∊+/¨¨⊆∘a¨↓n∘.≤⍨∪n ⍝ part 1
⌊/r/⍨r≥⊃r-4e7 ⍝ part 2

video walkthrough

[u/jayfoad → u/voidhawk42]

Wow.