I was unable to upload even the shortest video because it was too long for my instance. Therefore, please enjoy the following:

1. Partial visualization of test data. I cut this short because it took 40 seconds to do just a few (out of 81) paths: https://youtube.com/shorts/7UvzgSsMQNA
2. Partial visualization of full data. I cut this short because I didn't want to wait 40 minutes. It's sped up 2x by making it 60fps (each step is approximately one frame) https://youtu.be/cv9qSdrV2Z4
3. Full visualization, but it only shows the end paths, not individual steps: https://youtube.com/shorts/ozQ77ikI7JI

Unfortunately youtube is forcing my videos to be shorts due to aspect ratio and length, I don't know if I can force them to a regular video

Day 20: Race Condition

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Day 19 - Linen Layout

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I thought about it for 15 mins, but couldn't think of any mathematical tricks. I thought of lots of minor tricks, like comparing the number to the result and not adding any more multiplications if it's over, things that would cut 10%-20% here and there, but nothing which fundamentally changes big O running time.

For reference, here's my solution for part 2 in smalltalk. I just generated every possible permutation and tested it. Part 1 is similar, mainly I just used bit magic to avoid generating permutations.

(even if you haven't used it, smalltalk is fairly readable, everything is left to right, except in parens)

day7p2: in
	| input | 
	
	input := in lines collect: [ :l | (l splitOn: '\:|\s' asRegex) reject: #isEmpty thenCollect: #asInteger ].
	
	^ (input select: [ :line |
		(#(1 2 3) permutationsWithRepetitionsOfSize: line size - 2) 
			anySatisfy: [ :num | (self d7addmulcat: line ops: num) = (line at: 1)]
	]) sum: #first.

d7addmulcat: nums ops: ops
	| final |
	
	final := nums at: 2.
	ops withIndexDo: [ :op :i |
		op = 1 ifTrue: [ final := final * (nums at: i + 2) ].
		op = 2 ifTrue: [ final := final + (nums at: i + 2) ].
		op = 3 ifTrue: [ final := (final asString, (nums at: i+2) asString) asInteger ]
	].

	^ final

I wanted to get an idea of how the blocks were landing and here's some thoughts on what I came up with:

• they were building a simple maze (duh I guess).
• the final (blocking) block is highlighted as a tiny red dot for half a second or so (edit: now flashing!).
• my generated path jumped about seemingly at random even when blocks landed elsewhere so I don't animate the dropping of the first 1000 blocks as it's more noise than data.
• the ~500 blocks before the final one don't affect my path at all, so it's quite a boring end.
• Lemmy doesn't like long animations, so I skip 10 blocks at a time.

If you want to toast your CPU for a few seconds, here's some terrible Uiua code.

Data  ← ≡◇(⊜⋕⊸≠@,)°/$"_\n_" &fras "AOC2024day18.txt"
End   ← 70_70
Count ← 1024

D₄      ← [1_0 ¯1_0 0_1 0_¯1]
Valid   ← ▽¬⊸∊:▽⊸(≡/××⊃(≤⊢End|≥0))+D₄¤
BestLen ← ⍣(-1⧻⊢path(Valid|≍End)0_0↙:Data|∞)
Chop!   ← ◌⍢(⨬(⊙◌+1|⊙⊙◌:):⟜^0⌊÷2+,,|>)

BadBlock ← -1Chop!(=∞BestLen)Count ⧻Data
Skip     ← 1000
Step     ← 10
Times    ← ⍜(-Skip|⁅⍜(÷Step|⇡⌊))+1BadBlock

# paths - will ruthlessly spawn new threads until your CPU burns.
∵(×1_1_0)wait≡spawn(°⊚°□⊢path(Valid|≍End)0_0↙:Data)Times

¤∵(×0_0_1)⬚0+↯+1End0°⊚↙Skip Data           # old blocks
+:∵(×0_1_1)≡(⬚0+↯+1End0°⊚↘Skip↙)Times¤Data # add new blocks
≡+                                         # superimpose
⊂:⍜(⊡|⋅1_0_0) ⊡BadBlock Data⊣.             # Add frame for final block.
⍥(⊂:↙¯2.)10                                # Freeze frame.
≡(▽⟜≡▽4)                                   # Scale up.
&fwa "AOC2024day18.gif"gif 60

Day 18: Ram Run

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Full input link (it's kinda cool ngl): https://youtu.be/Jw3CXcaHZ0Q

I'll start with what I do not mean by this question. I know you need to know programming and data structures, but what I am asking about is specific algorithms and theorems.

The ones I can enumerate now (edited after some answers):

• BFS
• DFS
• Dijkstra's algorithm
• Chinese Reminder Theorem
• Dynamic Programming with memoisation or tabularisation
• operations on linked lists
• binary search
• Interval arithmetic
• GCD and LCM
• bitwise operations
• Topological sorting
• Shoelace formula
• mod inverse
• Linear algebra
• Priority queues
• Parsing algos
• Spectral decomposition

Mega guide link

Full input version here: https://youtu.be/itc7_HZmewQ

This poor guard must the fittest person in 1518. Man's doing a marathon every day

Day 17: Chronospatial Computer

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I had to stop for finals, so I'm way behind

Day 16: Reindeer Maze

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Day 15: Warehouse Woes

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So this is really kind of tangential, I am just messing around with the data and trying to at least nail down some basics so I can do sanity checks in my actual code. I am running into an odd discrepancy when trying to determine the number of times "XMAS" occurs in the input. I am only concerned with the straight forward matches, the instances of the substring "XMAS" appearing in the raw data.

When i do "grep -c XMAS input" or "rg -c XMAS input" they both show 107. But when I use regex101.com and search for the pattern XMAS, it shows 191 matches. Please help, I am truly at a loss here. While writing this, it occurred to me to just try using string.count("XMAS") in python on the data as a raw string, and it also returns 191. So really this question is more about grep and rp than anything. why are they only returning 107?

Day 14: Restroom Redoubt

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Day 13: Claw Contraption

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Day 12: Garden Groups

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