Advent of Code 2023 (Rust) 🎄




TIL (Today I learned)

Day 1

I alreayd got some experience in Advent of Code 2015 by practicing some of the days from that year, but needless to say I still need to learn a lot.

The borrow and owner system is still kind of aliën to me, but I am starting to get the hang of it. You can better read what the compiler says, because most of the time that fixes the issue that I have.

I also followed a video to setup VSCode Error Lens which shows what lines gives the error in VSCode for easy debugging. I am also using the Devcontainers extension together with Podman Desktop to run Rust, so you can easily launch the code yourself if you open the 2023 - rust folder.

Also HashMaps exist! I thought that it didn’t but you need to import it with use std::collections::HashMap; same as getting a substring with use substring::Substring; but for this you need to install a new crate with Cargo called substring with cargo add substring. It’s as easy as that.

And I really 😍 the println! macro (yes it’s called a macro), an example that I use almost every day:

println!("Day 1 ⭐1️⃣  result: {}", star1);

Where star1 can be used within the curly brackets like so: {star1} or after the fact, like in the example above.

Together with parsing numbers wich makes it easy as well, with "32".parse::<i32>().unwrap() (unless the string is not a number because I am not gracefully handling it at the moment). With these numbers I can already do some range parsing as well.

I forgot which language it was, but I think Python uses a bit of the same syntax almost. Where you can type something like 0..your_string.len() in a for-loop and it will get a number iterator.

Day 2

First time using a Regex in Rust, by default there is no implementation so going with the regex 📦. I also found out it is more limited then the one selected by default on Regex101 the hard way. So I had to redo some of the code eventually.

Day 3

Traits, traits and more traits. Comming from Java I wanted an equals (eq in rust) function. Seems like the #[derive(PartialEq)] does the job for me. So I then can use the contains function in an iterator. But also the Debug trait is really handy to have, now I can just println!("{:?}", struct) and it will print the struct like magic. No custom to_string() method required!

And casting is also super easy just do iter_y as i32 and most of the time it just works 🪄 like magic.

And lastly the enumarator with for (index, line) in lines.iter().enumerate() { to get a free index with your iterator.

Day 4

"Hello World!".split_once(" ") is really nice to use, as you can now do .unwrap().0 and always get the first result. Instead of doing "Hello World!".split(" ").nth(0).unwrap(). I also dabbled a bit in using .is_numeric() and more accendants.

Also to use HashMaps you need a special import, because it’s not enabled by default. To use a HashMap insert use std::collections::HashMap; somewhere at the top.

And I wasn’t done with the ranges, I found out that using an equals operator before the second number makes it inclusive, like so: 0..=10;

Day 5

For day five I did some searching for seeing how I can implement time into the project. With the chrono create it seemed easy enough. So doing chrono::offset::Local::now() to get the local datetime so I can print it to the console. I might later write something to compair both and see how long it took to run in seconds etc.

Today was also the day I found out about dereferencing, maybe a bit late but when you have a reference to a i32 variable you can do *variable to derefence the variable (from &i32 -> i32), this makes the code a bit cleaner as well but I need to read up on what it’s exactly doing. As I am not 100% convined that It will make a copy but just go to the original reference again. Also this doesn’t work for every struct/object as well. So use it sparingly.

This was also the first day where I had to use i64 because the number kept growing to much that it would overflow the i32.

Day 6

Ah the famed day six, I have a love hate relationship with this one. Here part two required 2 minutes to run on my laptop and 1 minute on my desktop at home. But in hindsight I had to program it differently still, then what I currently have made.

For example I tried to use multithreading with the Rayon crate using use rayon::prelude::*;. So actually use multiple cores. But before that I had to optimize the memory management of the application because it kept flowing over 16GB each time. The current implementation doesn’t go over 1.5GB in the container where I run Rust in. Apart from that I learned that the .iter() handles data per stream keeping the memory usage low (instead of multiple for-loops which is hard to read anyways).

Day 7

Day seven part one was a lot of fun to make, especially the different rules seeing regular Poker. On this day I learned how the sorting works in Rust and how to make a custom sorting function.

ranked_hands.sort_by(|a, b| match a.rank.cmp(&b.rank) {
        Ordering::Greater => Ordering::Greater,
        Ordering::Less => Ordering::Less,
        Ordering::Equal => {
            for index in 0..=4 {
                return match card_strength(, joker)
                    .cmp(&card_strength(, joker))
                    Ordering::Greater => Ordering::Greater,
                    Ordering::Less => Ordering::Less,
                    Ordering::Equal => continue,

We where supposed to rankt the cards by their match (5 of a kind is better then 4 of a kind) and if two hands have the same, then we check charachter per character to see what is the highest one.

Day 8

Day eight on the other hand was a lot easier again, although I did have to look up LCM (Least Common Multiple) and GCD (greatest common divisor) because I don’t really have a good Math background.

Day 9

I wanted to use pop on an array to remove the first item, I search and found the VecDeque which is basically a Vec but with some of the Queue functions. Also for part 2 it was really easy I only had to get the first item and actually do the calculation instead of doing a sum.

Day 10

Day 10 was kind of weird to do but I had some time issues and never got around it. This is the day where I got stuck because I was overthinking a lot.

Still working on part 2 though.

Day 11

I am finally taking a deeper dive in the world of modules, right now I have been copy pasting the whole code from the file to the appropriate file, like each time. But this is becomming bothersome now.

I found out that using mod works when running from the file. So using use aoc11; make my life easy so I can just call the run method on each day instead.

Advent of Code Repository