Advent of Code 2020 (4th week)

I started the 4th week of Advent of Code without having completed all the puzzles from week 3 yet. I missed part 2 of day 18 and both parts of day 20. Still, I think the best approach it to prioritise the daily riddle before trying to finish the missing ones. So, last week of Advent of Code 2020, here we go:

Day 21: Allergen Assessment#

After my fiasco on day 20, day 21 put me back on track. I solved the allergens problem with sets and set operations iterating my data until I got the ingredient for each allergen. It was a problem similar to day-16 (Ticket Translation).

And part 2 was really easy. I already got the data I needed from my part 1 solution (which got me thinking that maybe I missed a simpler solution for the first part, but whatever…)

👨‍💻 My solution

Day 22: Crab Combat#

I messed up a couple of times in my card’s combat with the small crab . First, I forgot to convert my input numbers to integers so I fell for the classic:

'4' > '32'

As if this wasn’t an issue in JavaScript as well… Then I used a recursive solution, which worked well for part 1 but it hit the maximum recursion depth in part 2 before I realised that the problem was perfectly suitable for an iterative approach and use recursion just for the sub-games instead of for every hand. And finally, I missed a key point of the instructions:

To play a sub-game of Recursive Combat, each player creates a new deck by making a copy of the next cards in their deck (the quantity of cards copied is equal to the number on the card they drew to trigger the sub-game).

I was using the whole deck to play the sub-game, and I lost a lot of time due to that error, because it was working perfectly for the test data but not for the real input.

👨‍💻 My solution

Day 23: Crab Cups#

Another round with the crab fella… I had issues to understand what was going on between moves 3 and 4 in the sample game, but after that it was easy to find a solution. The big problem appeared in part 2 because I used a list to represent the cups and of course, my solution couldn’t handle 10,000,000 iterations over 1,000,000 items. I tried a minimal optimisation by using a deque but it wasn’t enough and I just gave up the second star.

👨‍💻 My solution

Day 24: Lobby Layout#

I really enjoyed Christmas Eve’s puzzle. Mostly because I did it together with my SO. She’s been really supportive this whole month, asking about all the puzzles and so on. Even though she knows nothing about programming, we thought about the problem together and I was explaining step by step the code I was writing, trying to make it specially comprehensive. We had a good time and she really got a better understanding of what coding is all about after this.

The coordinates system we created to represent the tiles

The coordinates system we created to represent the tiles

👨‍💻👩🏻 Our solution

Day 25: Combo Breaker#

I appreciated that the last puzzle was that easy. The hardest part was understanding the instructions and figuring out that the subject number 7 was an arbitrary (it would probably be better called convenient) constant.

I got my 45th star and I understood that the 2nd for the day was only granted by having the previous 49. Fair enough!

👨‍💻 My solution


I’m really happy with my journey in this year’s AoC. I wouldn’t say that I’ve written the most Python-ish code, but after this four weeks I can now read and write basic programs fluently, which is definitely a level up for me! I had a good time, I suppose I improved a bit my problem solving skills (I confirmed that I need to dust off my algorithms and data structures books), and I ranked 25th in my company’s private leaderboard (sorted by number of stars) out of 61 people who got at least one star. Not bad! See you next year!