A solution in malbolge would be amazing and also kinda terrifying

You can actually use (singular) emojis as variable names. According to the documentation, they won't be be used as glyphs so you don't even have to worry about breaking changes of that kind :D

Hell yeah!

┻━┻︵ (°□°)/ ︵ ┻━┻

No worries, it does seem a lot less difficult in hindsight now, my mind just blanked at what I expected to be a lot more code :))

That performance improvement is amazing, I'll definitely take a look at how that works in detail later. Just gotta recover from the mental stretch gymnastics trying to remember the state of the stack at different code positions

Glad to hear that my attempts at de-spaghettifying worked to some degree at least :D

Uiua, forgot to put that in the post

Thanks to your solution I learned more about how to use reduce :D

My solution did work for the example input but not for the actual one. When I went here and saw this tiny code block and you saying

This turned out to be reasonably easy

I was quite taken aback. And it's so much better performance-wise too :D (well, until part 2 comes along in my case. Whatever this black magic is you used there is too high for my fried brain atm)

Uiua

Credits to @[email protected] for the approach of using reduce and also how to split the input by multiple characters.
I can happily say that I learned quite a bit today, even though the first part made me frustrated enough that I went searching for other approaches ^^

Part two just needed a simple modification. Changing how the input is parsed and passed to the adapted function took longer than changing the function itself actually.

Run with example input here

PartOne ← (
  &rs ∞ &fo "input-7.txt"
  ⊜□≠@\n.
  ≡◇(⊜□≠@:.)
  ≡⍜⊡⋕0
  ≡⍜(°□⊡1)(⊜⋕≠@ .)
  ⟜(⊡0⍉)

  # own attempt, produces a too low number
  # ≡(:∩°□°⊟
  #   ⍣(⍤.◡⍣(1⍤.(≤/×)⍤.(≥/+),,)0
  #     ⊙¤⋯⇡ⁿ:2-1⊸⧻
  #     ⊞(⍥(⟜⍜(⊙(↙2))(⨬+×⊙°⊟⊡0)
  #         ↘1
  #       )⧻.
  #       ⍤.=0⧻.
  #     )
  #     ∈♭◌
  #   )0)

  # reduce approach found on the programming.dev AoC community by [email protected]
  ≡(◇(∈/(◴♭[⊃(+|×)]))⊡0:°⊂)
  °□/+▽
)

PartTwo ← (
  &rs ∞ &fo "input-7.txt"
  ⊜(□⊜⋕¬∈": ".)≠@\n.
  ⟜≡◇⊢
  ≡◇(∈/(◴♭[≡⊃⊃(+|×|⋕$"__")]):°⊂)
  °□/+▽
)

&p "Day 7:"
&pf "Part 1: "
&p PartOne
&pf "Part 2: "
&p PartTwo

Uiua

Part one was simple enough. Part two nearly made me give up.
Part two has the most ugly and least performant code I've made in uiua so far but it gets the job done and that's all I care about for now.

Run with example input here

RotateClock ← (
  ⊙⊙(⍉⇌)
  ⊙(⇌⍜(⊡0)(-⊙(⧻⊡0.)+1))
  ↻¯1
)

RotateCounter ← (
  ⊙⊙(⇌⍉)
  ⊙(⍜(⊡0)(-⊙(⧻.)+1)⇌)
  ↻1
)

NewPos ← (
  ⊙⍜(⊙⊡:)(-1+⊙(⊗@#)⟜↘⊙.)⟜°⊟
  ⍜(⊡1)⋅
)

MarkPath ← (
  RotateClock
  ⍢( # replace characters up til next '#'
    ⊙(⊙⍜(↘⊙⊡:)(⍜(↙)(▽:@^⧻)⊗@#.)⟜°⊟
      NewPos
    )
    RotateCounter
  | ⋅(≠0⊡0))
  ◌◌
)

PartOne ← (
  &rs ∞ &fo "input-6.txt"
  ⊜∘≠@\n.
  # maybe make compatible with
  # non-up facing inputs
  ♭⊚=@^.
  [0 1 2 3]
  MarkPath
  &fwa "test.txt" json.
  /+/+=@^
)

PartTwo ← (
  &rs ∞ &fo "input-6.txt"
  ⊜∘≠@\n.
  # maybe make compatible with
  # non-up facing inputs
  ♭⊚=@^.
  [0 1 2 3]
  ◡MarkPath
  ⊙::
  # rotate the field to match the intital state
  ⊙⊙(
    ⊙(⊚=@#)
    ⍢(⇌⍉|¬≍⊚=@#)
    ⊙◌
  )
  ⊙⊙(⊚=@^.)
  ⊙⊙⊙¤∩¤
  ⊞(⊙⊙(⍜⊡⋅@#)
    RotateClock
    ⊙NewPos
    ¤¯1_¯1_¯1
    ⍢(⊙◡(⊂⊢)
      ⊂
      ⊙(RotateCounter
        ⊙NewPos
      )
    | =1+⊙(∈↘1⇌)◡⋅(≠129⊡2)⊙(⊂⊢))
    # 129 = length of input array. Hardcoded because
    # the condition block doesn't seem to get the
    # input array passed to it so the length can't
    # be read dynamically
    ⊙(⊂⊢)
    ∈
    ⊙◌
  )
  /+♭
)

&p "Day 6:"
&pf "Part 1: "
&p PartOne
&pf "Part 2: "
&p PartTwo

Uiua

This is the first one that caused me some headache because I didn't read the instructions carefully enough.
I kept trying to create a sorted list for when all available pages were used, which got me stuck in an endless loop.

Another fun part was figuring out to use memberof (∈) instead of find (⌕) in the last line of FindNext. So much time spent on debugging other areas of the code

Run with example input here

FindNext ← ⊙(
  ⊡1⍉,
  ⊃▽(▽¬)⊸∈
  ⊙⊙(⊡0⍉.)
  :⊙(⟜(▽¬∈))
)

# find the order of pages for a given set of rules
FindOrder ← (
  ◴♭.
  []
  ⍢(⊂FindNext|⋅(>1⧻))
  ⊙◌⊂
)

PartOne ← (
  &rs ∞ &fo "input-5.txt"
  ∩°□°⊟⊜□¬⌕"\n\n".
  ⊙(⊜(□⊜⋕≠@,.)≠@\n.↘1)
  ⊜(⊜⋕≠@|.)≠@\n.

  ⊙.
  ¤
  ⊞(◡(°□:)
    ⟜:⊙(°⊟⍉)
    =2+∩∈
    ▽
    FindOrder
    ⊸≍°□:
    ⊙◌
  )
  ≡◇(⊡⌊÷2⧻.)▽♭
  /+
)

PartTwo ← (
  &rs ∞ &fo "input-5.txt"
  ∩°□°⊟⊜□¬⌕"\n\n".
  ⊙(⊜(□⊜⋕≠@,.)≠@\n.↘1)
  ⊜(⊜⋕≠@|.)≠@\n.
  ⊙.
  ⍜¤⊞(
    ◡(°□:)
    ⟜:⊙(°⊟⍉)
    =2+∩∈
    ▽
    FindOrder
    ⊸≍°□:
    ⊟∩□
  )
  ⊙◌
  ⊃(⊡0)(⊡1)⍉
  ≡◇(⊡⌊÷2⧻.)▽¬≡°□
  /+
)

&p "Day 5:"
&pf "Part 1: "
&p PartOne
&pf "Part 2: "
&p PartTwo

Uiua

This one was nice. The second part seemed quite daunting at first but wasn't actually that hard in the end.

Run with example input here

Row    ← ⌕ "XMAS"
RevRow ← ⌕"SAMX"
Sum    ← /+/+
Count  ← +∩Sum⊃Row RevRow

PartOne ← (
  &rs ∞ &fo "input-4.txt"
  ⊜∘≠@\n.
  ⊙+⟜∩Count⟜⍉ # horizontal and vertical search
  ⟜(/+⧈(Count⍉≡⬚@ ↻⇡⧻.)4)
  /+⧈(Count⍉≡⬚@ ↻¯⇡⧻.)4
  ++
)

Mask ← °⊚×2⇡5
# Create variations of X-MAS
Vars ← (
  ["M S"
   " A "
   "M S"]
  ≡♭[∩⟜⍉]≡⇌.
  Mask
  ⊏0⊞▽¤
)

PartTwo ← (
  &rs ∞ &fo "input-4.txt"
  ⊜∘≠@\n.
  ⧈(/+♭⊞≍⊙¤Vars▽Mask♭)3_3
  Sum
)

&p "Day 4:"
&pf "Part 1: "
&p PartOne
&pf "Part 2: "
&p PartTwo

Uiua

Regex my beloved <3

Run with example input here

FindMul ← regex "mul\\((\\d+),(\\d+)\\)"

PartOne ← (
  &rs ∞ &fo "input-3.txt"
  FindMul
  /+≡(×°⊟⋕⊏1_2)
)

IdDont ← ⊗□"don't()"♭

PartTwo ← (
  &rs ∞ &fo "input-3.txt"
  regex "mul\\(\\d+,\\d+\\)|do\\(\\)|don't\\(\\)"
  ⍢(IdDont.
    ↘1⊃↘↙
    ⊗□"do()"♭.
    ⊂↘1↘
  | IdDont.
    ≠⧻,
  )
  ▽♭=0⌕□"do()".
  ≡(×°⊟⋕⊏1_2♭FindMul)♭
  /+
)

&p "Day 3:"
&pf "Part 1: "
&p PartOne
&pf "Part 2: "
&p PartTwo