Today’s challenge rather appeals to me as a folk dancer, because it describes a set of instructions for a dance and asks us to work out the positions of the dancing programs after each run through the dance. → Full code on GitHub !!! commentary So, part 1 is pretty straight forward: parse the set of instructions, interpret them and keep track of the dancer positions as you go. One time through the dance. Read more...

Today’s challenge introduces two pseudo-random number generators which are trying to agree on a series of numbers. We play the part of the “judge”, counting the number of times their numbers agree in the lowest 16 bits. → Full code on GitHub Ever since I used Go to solve day 3, I’ve had a hankering to try the other new kid on the memory-safe compiled language block, Rust. I found it a bit intimidating at first because the syntax wasn’t as close to the C/C++ I’m familiar with and there are quite a few concepts unique to Rust, like the use of traits. Read more...

Today’s challenge has us helping a disk defragmentation program by identifying contiguous regions of used sectors on a 2D disk. → Full code on GitHub !!! commentary Wow, today’s challenge had a pretty steep learning curve. Day 14 was the first to directly reuse code from a previous day: the “knot hash” from day 10. I solved day 10 in Haskell, so I thought it would be easier to stick with Haskell for today as well. Read more...

Today’s challenge requires us to sneak past a firewall made up of a series of scanners. → Full code on GitHub !!! commentary I wasn’t really thinking straight when I solved this challenge. I got a solution without too much trouble, but I ended up simulating the step-by-step movement of the scanners. I finally realised that I could calculate whether or not a given scanner was safe at a given time directly with modular arithmetic, and it bugged me so much that I reimplemented the solution. Read more...

Today’s challenge has us helping a village of programs who are unable to communicate. We have a list of the the communication channels between their houses, and need to sort them out into groups such that we know that each program can communicate with others in its own group but not any others. Then we have to calculate the size of the group containing program 0 and the total number of groups. Read more...

Today’s challenge is to help a program find its child process, which has become lost on a hexagonal grid. We need to follow the path taken by the child (given as input) and calculate the distance it is from home along with the furthest distance it has been at any point along the path. → Full code on GitHub !!! commentary I found this one quite interesting in that it was very quick to solve. Read more...

Today’s challenge asks us to help a group of programs implement a (highly questionable) hashing algorithm that involves repeatedly reversing parts of a list of numbers. → Full code on GitHub !!! commentary I went with Haskell again today, because it’s the weekend so I have a bit more time, and I really enjoyed yesterday’s Haskell implementation. Today gave me the opportunity to explore the standard library a bit more, as well as lending itself nicely to being decomposed into smaller parts to be combined using higher-order functions. Read more...

In today’s challenge we come across a stream that we need to cross. But of course, because we’re stuck inside a computer, it’s not water but data flowing past. The stream is too dangerous to cross until we’ve removed all the garbage, and to prove we can do that we have to calculate a score for the valid data “groups” and the number of garbage characters to remove. → Full code on GitHub Read more...

Today’s challenge describes a simple instruction set for a CPU, incrementing and decrementing values in registers according to simple conditions. We have to interpret a stream of these instructions, and to prove that we’ve done so, give the highest value of any register, both at the end of the program and throughout the whole program. → Full code on GitHub !!! commentary This turned out to be a nice straightforward one to implement, as the instruction format was easily parsed by regular expression, and Python provides the eval function which made evaluating the conditions a doddle. Read more...

Today’s challenge introduces a set of processes balancing precariously on top of each other. We find them stuck and unable to get down because one of the processes is the wrong size, unbalancing the whole circus. Our job is to figure out the root from the input and then find the correct weight for the single incorrect process. → Full code on GitHub !!! commentary So I didn’t really intend to take a full polyglot approach to Advent of Code, but it turns out to have been quite fun, so I made a shortlist of languages to try. Read more...