Classic

In the last post that was like a month ago ( An emote ) I mentioned how I was busy and couldn’t work on ChompChomp. Well, I’m still busy, and while I thought it was calming down before turns out it wasn’t.

I’m still trying to make time for ChompChomp, and actually have been working on it, just haven’t had the time to write about it. But I’ve been planning to partake in the Advent of code this year and do a bit of writing about it as I go, so here we are!

Not sure how frequent I’ll post about it, but I’ll do what I can! I heard it gets really hard too which is exciting but also means I probably won’t solve one per day forever. Anyway let’s dive in!

What is Advent of Code?

Advent of Code is a yearly event where every day from December 1st to December 25th, a new programming puzzle is released. The puzzles are themed around Christmas and are usually pretty fun to solve. I’ve never done it before but I’ve heard a lot about it and figured this year I’d give it a shot!

That’s the gist of it! These posts will contain spoilers for the puzzles, so if you’re doing it yourself and don’t want spoilers, don’t read these posts until you’ve solved the puzzle yourself! Or if you want some hints or are curious about how I solved it, then read on!

Also these posts will be showing my process at arriving at a solution, with the mistakes and all that so not everything I show will be the best way to do it, just how I initially went at it.

Day 1

From the start I knew I was going to do this in typescript, and so the first thing to do real quick was just a bit of simple setup.

Also if you wanna follow along advent of code is free! Just head over to the website and login with your github to get started.

Project Setup

Normally for typescript you gotta init the folder with npm (pnpm An emote ) but with deno I just run deno init and I’m ready to code.

I figured I can have a directory with ts files for each day, and then run them from main.ts so that way I don’t need to constantly change my dev script’s target file.

Current setup is:

- 📂 data
- 📂 src
  - 📄 day1.ts
  - 📄 day1_test.ts
- 📄 main.ts
- 📄 deno.json
- 📄 deno.lock

The day1_test.ts is a file where I’ll write some tests for a couple functions from day1.ts to test what I’m writing. All set to start coding!

The Problem

First thing to do is read day 1’s problem in it’s entirety and understand the task at hand. I’ll summarize it here but if you wanna read it yourself, here’s the link.

First up was a quick explanation of how things work, 1 puzzle each day, separated into two parts. Solving each gives you a star, and the goal is to get as many stars as possible.

Then we dive into the puzzle itself!

Puzzle 1 Part A

The scenario is that Christmas elves have given me a map where all the 50 stars are located (2 for each 25 days) I’ve got to go around and collect the stars, and to reach the spots on the map I’m being loaded into a Trebuchet and launched to them. Before launching though I need to fix some launch calculations that a newer elf messed up.

The calculation involves taking in a bunch of strings containing numbers, I need the first & last digit (in that order), then those digits need to be combined into a number, and all numbers need to be added together. Here’s the bit verbatim:

The newly-improved calibration document consists of lines of text; each line originally contained a specific calibration value that the Elves now need to recover. On each line, the calibration value can be found by combining the first digit and the last digit (in that order) to form a single two-digit number.

Then we’re given an example of what the input & output:

1abc2
pqr3stu8vwx
a1b2c3d4e5f
treb7uchet

In this example, the calibration values of these four lines are 12, 38, 15, and 77. Adding these together produces 142.

So for the first line, 1abc2, the first digit is 1 and the last digit is 2, so we combine them to get 12. Then we do that for each line, and add them all together to get the final answer. Got it! One ‘tricky’ thing to note, for that last input treb7uchet the 7 is repeated as both the first & last digit since there’s only one digit in the string.

Then I’m given my own personal input (everyone gets their own inputs) as a text file, with about 1000 lines of that sort of text.

Alright so time to break down this sort of parsing into steps.

Get the first digit
Get the last digit
Combine them into a number
Add all the numbers together

I got to work! When it comes to strings, I’m a fan of regex so my mind went right to that. Since we’re matching just digits it ends up being a trivially simple regex: /[0-9]/g which matches all digits in a string.

Then I just need to get the first & last digit, and to do that, I can just use the match method on the string with the regex, and grab the first & last digit from the resulting array.

Let’s slap that into a function called firstLastNum that does exactly that for any given string:

export const firstLastNum = (s: string): [number, number] | undefined => {
  // Our digit regex
  const r = /[0-9]/g;

  const matches = s.match(r);

  // `match` returns `null` if no matches are found so this is just quick bit of type narrowing to let typescript know we've got a match past this point, even though I know it will always have a match.
  if (!matches) {
    console.log('No digits in string, ', s);
    return;
  }

  // The `.at` method is just a nice way of indexing arrays, -1 is the last thing in an array
  const left = matches.at(0);
  const right = matches.at(-1);

  // More type narrowing here too
  if (!left || !right) {
    console.log('Could not get nums from matches', matches);
    return;
  }

  // Specifying the return as a tuple type since we will always have two digits.
  return [left, right].map(Number) as [number, number];
};

Why return numbers? I wanted this function to do only one thing: Take a string, and return the first & last digits in that string. And I did this right after I woke up so when I was writing it my brain thought “return digits mean need to be numbers” so I went and returned em as numbers.

Testing `firstLastNum`

So I mentioned before I’d do a smidgen of test writing since it’s so seamless in Deno, and I did! I wrote a couple tests using the example inputs to make sure it works as expected. Here’s what that looks like:

const toRes = (inp: number[] | undefined) => inp as unknown as ArrayLike<number>;

Deno.test(function firstLastNumTests() {
  const res1 = firstLastNum('1abc2');
  const res2 = firstLastNum('par3stu8vwx');
  const res3 = firstLastNum('a1b2c3d4e5f');
  const res4 = firstLastNum('Trebu7chet');

  assertArrayIncludes(toRes(res1), [1, 2]);
  assertArrayIncludes(toRes(res2), [3, 8]);
  assertArrayIncludes(toRes(res3), [1, 5]);
  assertArrayIncludes(toRes(res4), [7, 7]);
});

Why the whole toRes bit? Well since I did a bit of narrowing in the function, typescript doesn’t know that the return will always be an array of numbers, so I just use that helper function to cast it to that type make the compiler happy.

All passing! So then I just read the input file, ran this on every line, combined the numbers and summed. The code for that is nothing special honestly. I then submit my answer based on the input and it worked first try!

Puzzle 1 Part B

The next bit was almost the same thing, but now we also have digits as words! So something like:

two1nine

It told me “my answer is close but not quite right” and this confused me. At this point I had even more test cases, and they all were passing. It suggested checking the reddit for hints, and lo’ and behold, the top post was “if you’re stuck on part 2 try this input: eighthree” which should yield [8, 3] but my code was returning [8,8].

Day 2 soon!

Advent of Code 2023 Day 1