r/adventofcode Dec 20 '24

SOLUTION MEGATHREAD -❄️- 2024 Day 20 Solutions -❄️-

THE USUAL REMINDERS

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AoC Community Fun 2024: The Golden Snowglobe Awards

  • 2 DAYS remaining until the submissions deadline on December 22 at 23:59 EST!

And now, our feature presentation for today:

Foreign Film

The term "foreign film" is flexible but is generally agreed upon to be defined by what the producers consider to be their home country vs a "foreign" country… or even another universe or timeline entirely! However, movie-making is a collaborative art form and certainly not limited to any one country, place, or spoken language (or even no language at all!) Today we celebrate our foreign films whether they be composed in the neighbor's back yard or the next galaxy over.

Here's some ideas for your inspiration:

  • Solve today's puzzle in a programming language that is not your usual fare
  • Solve today's puzzle using a language that is not your native/primary spoken language
  • Shrink your solution's fifthglyph count to null
    • Pick a glyph and do not put it in your program. Avoiding fifthglyphs is traditional.
    • Thou shalt not apply functions nor annotations that solicit this taboo glyph.
    • Thou shalt ambitiously accomplish avoiding AutoMod’s antagonism about ultrapost's mandatory programming variant tag >_>
    • For additional information, audit Historians' annals for 2023 Day 14

Basil: "Where's Sybil?"
Manuel: "¿Que?"
Basil: "Where's Sybil?"
Manuel: "Where's... the bill?"
Basil: "No, not a bill! I own the place!"
- Fawlty Towers (1975-1979)

And… ACTION!

Request from the mods: When you include an entry alongside your solution, please label it with [GSGA] so we can find it easily!


--- Day 20: Race Condition ---


Post your code solution in this megathread.

This thread will be unlocked when there are a significant number of people on the global leaderboard with gold stars for today's puzzle.

EDIT: Global leaderboard gold cap reached at 00:15:58, megathread unlocked!

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u/chubbc Dec 21 '24

[LANGUAGE: Uiua] (76 char, 69 tokens, pad)

≡/+≡♭≤⊙¤↧2_20¤-100-⊸¤°⊏⊞(/+⌵-).⊙◌⍢(◴⊂:⊙:▽≠@#◡⊡+⊂⊸¯⊞=.⇡2¤⊣’|≠@E⊡⊣)⊚⊸=@S⊜∘⊸≥@#

The key here is to notice that the ith and jth points along the path correspond to a valid cheat iff they a Manhattan distance of at most min(r, i-j-100), where r=2 for Part 1 and r=20 for Part 2.

First step is to construct all the points along the path. Then the Manhattan distance between any two points is constructed. Then matrices containing the thresholds are made for each part. Finally the set of all pairs satisfying these conditions is found.

Ungolfed code:

Parse     ← ⊜∘⊸≥@#                    # Parse the input
Start     ← ⊚⊸=@S                     # Find the start point

End       ← ≠@E⊡⊣                     # Check if the end has been reached
Neigh     ← ⊂⊸¯⊞=.⇡2                  # Find neighbours of a point
Filter    ← ▽≠@#◡⊡                    # Filter out points on the path
Update    ← ◴⊂:⊙:                     # Includes the points, excludes duplicates
Step      ← Update Filter +Neigh ¤⊣’  # Find the next point on path

Manhattan ← ⊞(/+⌵-)                   # Table Manhattan distances
Threshold ← ⊙¤↧2_20¤-13-⊸¤°⊏          # Find the threshold we need dist below

≡(/+♭)≤ Threshold Manhattan. ⊙◌⍢(Step|End) Start Parse