Day 22 of Advent of Code 2021 was all about cubes. The problem statement provided us with coordinates of cubes and an “on” or “off” instructions. These instructions needed to be carried out in order. The first part of the problem was deceptively simple. So much so that I didn’t go for the “obvious” solution initially because I thought it wouldn’t scale. As it happened I ended up implementing it anyway as my optimised approach wasn’t working because I made a simple mistake.

On Day 21 of Advent of Code 2021 we played Dirac Dice! And part one felt way too easy to solve, but I needed have worried because part two we were asked to solve a limited multiverse problem. And without a quantum computer! The problem The problem was described as follows. Two players are playing a game with three dice Each starts on a different position of the board The board is circular and has 10 numbered positions Players take it in turn to roll three dice A player moves forward by the sum of those three dice Once the complete their move, they add as many points to their score as indicated by the board position First to 1000 points wins The dice are deterministic, meaning that they roll 1, 2, 3, …, 100, 1, 2, … Part One To start with, I created some types:

Hmpf. It’s now January and I’m still doing Advent. Still, I was determine to push ahead. Then I got stuck good and proper on Day 19 - though to be fair the whole Log4shell dumpster fire was taking up a lot of time, so I decided to skip it for now. Day 20 of Advent of Code 2021 was all about transforming images. What made it slightly more complicated was the fact that the images were nominally of infinite size.

Day 18 of Advent of Code 2021 took rather a long time to get right. Half of the problem was that there were a couple of gotchas in the requirements and the choice of data structure hugely impacted how easy it was to come up with a solution. Just like Day 17 I was using TDD and this helped me root out some blind alleys nicely. The problem The story was roughly as follows: In order to continue on the Advent of Code submarine journey, we had to solve snailfish number problems.

On day 17 of Advent of Code 2021, I did something that I should have really done from the start: Write tests first. My excuse so far has been that I wasn’t familiar with Haskell yet and other such lame excuses. As a software engineer, I should know better. TDD doesn’t slow me down, it makes things faster. The last straw - if you like - was when I was writing up my exploits from Day 16 and I thought there really is no excuse for not testing these parser combinators individually.

For day 16 Advent of Code 2021, it was all about monadic parser combinators (whatever they are)! Just like Day 15, this one took me a lot longer to complete than I had wanted, this time it was all about learning Haskell’s approach to parsing text. According to the story, we had to decode a message in a custom binary format, the Buoyancy Interchange Transmission System (BITS). BITS is a message format that encodes both literal values and operations.

Advent of Code 2021 day 15 took us back to the 2-dimensional maps we first encountered on Day 11 and Day 9. We had to parse a map again, and this time we had to find the shortest path from the top left to the bottom right. This was the first time when a homespun algorithm just did not cut the mustard, and I had to wrack my brain (i.e. use Google) to do a bit of algorithm research.

After Advent of Code 2021 transparent origami on Day 13 with more output than just a number, for Day 14 it was back to more standard processing with exponential complexity. Interestingly in part 1 I initially started going down the route of not trying to brute forcing it, got almost there but tangled myself in some logic, so I decided to “sod it, I’ll just brute force it” only to then throw the brute force solution away again as soon as I got to part 2.

On day 13 of Advent of Code 2021 we had to do the impossible. We were folding a transparent piece of paper 12 times. Surely it isn’t possible to fold paper more than 7 times, but we also have to remember that we’re in a Santa submarine! The aim of the puzzle is to get a code by folding over a transparent sheet of paper which has got dots dotted all over.

For Advent of Code 2021 day 12 it took me a while to get going though for reasons unrelated to coding, Norovirus is not pleasant! So when I finally did the puzzle, I didn’t find it as difficult as I thought it would be based on some of the messages on the #adventofcode channel. The puzzle started with With your submarine’s subterranean subsystems subsisting suboptimally This deserves a medal in itself.