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- Philipp Ludewig

Advent of Code 2021 Day 1

Aloha people,

it's the time of the year again where coding elves earn some internet points and learn cool stuff while doing that. Ofc I am talking about advent of code. This year I want to use a recently learned language and re-visit some I haven't used in a while. I also try to pair with some colleagues on the puzzles as I am still on the beach and this are the perfect coding exercises between the cloud provider workshops.

In these years advent of code the story starts with a careless elf who has dropped the sleigh keys into the ocean. Ohhh no! Good that the elves have a submarine ready to go!

Day one informs us that the sonar sweep has returned some results (our puzzle input) and now we need to find the count of increases in these measurements. I have chosen to use Rust for this one. The code can be found here.

My approach to the first part of the puzzle was rather simple:

  • Read in the file as a vector of u32
  • Iterate over the measurements and increase a counter when ever there is an increase
  • Profit

Interestingly is that it was my first time using IntelliJ to create the Rust project, and it took me no time to get first results. I just wonder whether all unit tests are to be put into the production class itself, for now I am following what I see in the Rust workshops I have visited. Here is the method for part one of the puzzle. We expect a reference from a vector which contain unsigned numbers. I am still a beginner with this language so the decision whether to use i32 or u32 I made simply because all values in the puzzle input were positive.

fn count_increases_of_measurements(measurements: &Vec<u32>) -> u32 {
    let mut count_of_increases: u32 = 0;
    let mut latest_increased_measurement: &u32 =

    for measurement in measurements {
        if measurement > latest_increased_measurement {
            count_of_increases = count_of_increases.add(1)
        latest_increased_measurement = measurement;

    return count_of_increases;

Now that solved part one of the puzzle only so that part two could give me a headache, but Rust came to the rescue. The new puzzle is to implement a sliding window over the vector so that we can calculate the sum of it's tuple. Let me visualise this:

199  A      
200  A B    
208  A B C  
210    B C D
200  E   C D
207  E F   D
240  E F G  
269    F G H
260      G H
263        H

The puzzle is to calculate the sum of 199,200,208 and then switching to the next tuple 200,208,210 and so on. I never have seen this kind of problem, and so I was wondering for a short time how to solve this. In the end it's not really hard. You would create slices from the vector and save the sum of them to another vector. I was fiddling around with the vector as Rust showed me this great method windows(n). It creates a list of tuples which I could just add up to get the sum. Voilà and so I had solved part two of day one.

fn collect_sum_of_triple_measurements(measurements: &Vec<u32>) -> Vec<u32> {
 let triples = measurements.windows(3);
 let mut collection_sums:Vec<u32> = Vec::new();
    for triple in triples {
        let sum = triple.iter().sum();

    return collection_sums
pub enum State {

impl From<&'a str> for State {
    fn from(s: &'a str) -> Self {
        match s {
            "start" => State::Start,
            "closed" => State::Closed,
            _ => unreachable!(),

That's it for day one so far. Write me in the comments how exited you are!