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.

Advent of Code 2021 day 11 felt a little bit like a repeat of Day 9. In both cases, we got a 2-dimensional map with single digit values. In case of day 9 it was a height map, this time round we’ve got a 10x10 grid of bioluminescent Octopi. Each of those critters has an energy level that increases each round. Once that level goes past 9, it lets off a flash, which then imparts extra energy into the surrounding 8-legged creatures.

Day 10 of Advent of Code 2021 was all about mismatched brackets. And I think Haskell did rather well on this as I found the expressiveness arrived at a really concise solution. We’re still in our Advent submarine and after mapping the floor on Day 9, we now discover lots of syntax errors in the submarine navigation system. The problem This puzzle was all about matching brackets, the input was like this:

Dave Farley and Martin Fowler are two heavyweights when it comes to Software Development. As well as his latest and hugely anticipated book Modern Software Engineering, Dave wrote Continuous Delivery. Martin co-wrote the Agile Manifesto and Refactoring. All of which are hugely influential to large swathes of software engineers. So when both came together for Dave’s new series on YouTube, the Engineering Room (sponsored by Equal Experts), it was bound to be very interesting.