AoC 2018 – Day 10 Retro

Today is day 10 of Advent of Code 2018, the fun daily coding challenge I mentioned I was taking part in this year, and I thought it a good time to take a quick look back at my story so far.

I’ve still not managed to rank globally for any of the challenges (the closest I came was on day 5 when I completed part two 696th) but things are going reasonably well on our private BJSS leaderboard, and the challenges have mostly been fun. So far I’ve stuck with Ruby as my language of choice, although I almost broke out Unity 2D for today’s graphical challenge (Early-morning me obviously had grand ideas which were quickly set aside when I realised I could zoom out my terminal and stick with Ruby).

Here’s a quick rundown (with possible mild spoilers) of the challenges to date. The links take you to my solutions on GitLab, which obviously do contain spoilers, so don’t click them if you haven’t already done the puzzle for that day.

• Day 1 was a very simple problem involving summing a list of numbers, and finding the first duplicated number. Nothing much to say here, nice and quick.
• Day 2 involved finding characters duplicated two- and three-times in a string, with part two focusing on finding strings that differed by one character. I went with hash-based solutions for this one.
• Day 3 was about finding overlapping rectangles. I made a simulation for this as the maths escaped me. This was the first solution that was properly object-oriented Ruby, and I got stuck for a while because I accidentally transposed my X and Y coordinates in one of the methods!
• Day 4 involved finding the guard who slept the most, and (in part two) the minute in which they were most often asleep. Another simulation (I quite enjoyed this one).
• Day 5 was about reducing a string by removing pairs until none remained. Regex and recursion to the rescue here – a really quick solution.
• Day 6 was, frankly, a nightmare. I couldn’t really visualise the problem at first, and it took me a lot longer than it should have to really get to grips with it. Solved in the end, but after many hours on-and-off. I did learn something new though 🙂
• Day 7 involved a dependency graph and another simulation. I had a lot of fun with this, and even made an ANSI-based visual mode so you could watch the simulation unfold in the terminal. Great fun.
• Day 8 was a simple tree problem involving both breadth-first and depth-first traversal. The depth-first part had a little twist that meant it took a little thinking about.
• Day 9 caused me a few problems – partly due to some vague wording in the puzzle, and partly due to my not understanding the problem properly for a while. It was made worse by the fact that I initially decided to write it with the wrong data-structure because I felt it would be quicker. After a few false starts I gave up on that and finally made it work using circular linked lists.
• Day 10 was another fun one involving points and velocities to work out when the points (stars) align to display a message. Initially I planned to switch to something with proper graphical support (in a fit of complete overkill, I fired up Unity) but settled in the end on a Ruby solution after I realised I could make the output fit in a terminal.

And that’s it so far! The most fun I’ve had so far was probably on day 7, while my least favourite has been day 6.

Taking part? Let me know in the comments what your favourite puzzle has been thus far.