Advent of Code 2024 - Day 9

Stuck in Part 2. My algo works for the sample input, but not the real input. Any help?

https://github.com/Aetherus/advent-of-code/blob/0bc39c89cdd8d327fac4aab63b74b828ea2b15f4/2024/day-09.livemd

It took me a long time to find an off-by-one error in part 2. The combined runtime for both parts is 0.4 seconds.

https://github.com/bjorng/advent-of-code/blob/main/2024/day09/lib/day09.ex

Finally found the problem. I should not swap a file with a space behind that file.

https://github.com/Aetherus/advent-of-code/blob/178d10a0a3429953ed8fff3df1bca5b3d582e9cb/2024/day-09.livemd

My solution takes 11 seconds adventofcode/lib/solutions/2024/day09.ex at main · lud/adventofcode · GitHub

I have an entry in the disk (a map) for each block. I will see if I can keep all contiguous file parts as a single map entry.

I am not proud of the code I wrote today.

I totally misunderstood the part 2 problem, came up with some code that gave the right answer anyway somehow but it was too slow, so I rewrote it after actually understanding what I was supposed to do, but it was even slower, so I scratched my head a bit and then rewrote it again.

For such an innocuous-sounding puzzle, that did my head in.

https://github.com/sevenseacat/advent_of_code/blob/main/lib/y2024/day09.ex

Runtime:

Name                     ips        average  deviation         median         99th %
day 09, part 1          9.26      108.03 ms     ±0.66%      107.88 ms      111.50 ms
day 09, part 2          7.28      137.37 ms     ±0.68%      137.22 ms      139.75 ms

Very slow solution today. I might come back optimizing it:

https://github.com/Flo0807/adventofcode/blob/main/2024/09.livemd

again just scrolling ultra fast down to not see any spoilers .. is there a bug in day 9 description?

The first example above, 2333133121414131402, represents these individual blocks:

00...111...2...333.44.5555.6666.777.888899

but:

left: “00…111…2…333.44.5555.6666.777.8888..99”
right: “00…111…2…333.44.5555.6666.777.888899”

i just made the function by spec …

for extremely simple algo that fails see here https://github.com/jarlah/advent_of_code/blob/master/lib/2024/day_9/Part1.ex#L9

ill eat my hat if it isnt something do with the pattern matching for the parse function … i have even added more tests that prove the more simpler examples is parse correctly

No. The example ends with 402 so there’s 4 eights, 0 gap, and 2 nines.

What does your code here https://github.com/jarlah/advent_of_code/blob/master/lib/2024/day_9/Part1.ex#L28 do if n2 is zero?

Your 90909 example is also wrong - it should be 000000000111111111222222222. The description says:

A disk map like 90909 would represent three nine-block files in a row (with no free space between them).

ofc duh! thanks

There’s been an bug in the problem on only one day that I can remember, in ten years of AOC. And there was a mad uproar about that and it was fixed within an hour.