This is my repository for the Advent of Code challenges.

I will be using Python 3.11 for this, in the hope to learn more advanced features of the language.

Part 1 was pretty easy, make a list of characters and use the first and last character of each line to make a number. Then add all the numbers together.

Part 2 was a bit more difficult, first it enumerates forward and backward to find the first digit and it records the position of both. Then it uses a dictionary and find to see if there is an earlier digit (comparing positions) and rfind to see if there is a later digit. If there is, the new characters are recorded, joined, and then summed for an answer.

• Using line[::-1] to reverse a string
• rfind to find strings in reverse

The big challenge here was parsing the strings into a usable format. I've used a lot of nested loops here so nowhere near as efficient as i would like, however a dirty solution still works. I might come back to this and try and improve it.

I was making some stupid mistakes with the way i set it up, particularly having the valid_games list which i initially set the range to constant values. Obviously then when the list changes size (testing) nothing works properly... I also broke out the logic checking into separate variables in order to make the debugging easier (thanks breakpoints, really useful here)

Due to other commitments, I was >24 hours late to this one, unfortunately this makes the personal leaderboard a bit pointless. I might start using a stopwatch from now on to get a better idea of how long it takes me to complete each challenge. It kind of helps being in a different timezone, it comes out at 6pm for me which is inconvenient but that's not as bad as 12am for some people!

• READ THE TASK - I made a bunch of stupid mistakes while working on it
• I need to learn more about breaking out of loops, too many nested loops and removing IDs from a list isn't ideal
• Could I be using regex here? Probably but I don't know how to use it yet

Well, I really need to work on my grid logic. I made a grid, and set up a check offsets function to test if a given position was valid (i.e had a symbol adjacent) and used that.

One of the challenges i faced was trying to account for part numbers being multiple digits long. It took a while to get it to iterate forward to find the end of the number, and it then tests the offsets for each position the number occupies. I also had to change the way i iterated through the list, when using a for loop it would catch the end of part numbers, i.e. given 123# it finds 123, then 12, then 1. I changed it to a while loop and it works fine now.

Then part 2 was a real change, I spent too long trying to figure out a solution to it and eventually gave up and looked at the subreddit. I'm not sure i would have come up with the solution on my own, but i'm glad i saw it. At some point i'll come back to this and try and figure out a solution on my own, but for now i'm happy to move on and get some sleep.

• Grid logic is hard

Part 1 was fairly trivial, once I got the string comprehension working. I'm not sure if there is a better way to do it, but it works so I'm happy with it. Although it took a bit of hitting my head against a wall to understand how to translate that "first match makes the card worth one point and each match after the first doubles the point value of that card." into code.

Part 2 was more tricky, my initial solution ran for ~10 minutes, generating list 10s of millions of items long so it must have got stuck in a loop somewhere.

After a couple hours, I decided to give up and look at the subreddit for an answer. I've seen defaultdict mentioned a few times, but never used it myself, might be something to look into.

• defaultdict - What is it, how does it work, and how can i use it?
• Translating maths into code
• Adding items to the list that is being iterated through is a bad idea, leads to infinite loops and sadness