Advent of Code 2022

Some solutions to the Advent of Code challenge (https://adventofcode.com/)

YouTube videos of selected solutions

After solving the puzzles I go and check videos of some of the leaderboard contributers (often just picking the first that comes up from the search). I do this to try to learn about different approaches to attacking the problem, language features I don't know and the use of additional packages.

Day 5

https://www.youtube.com/watch?v=Fg7wLU5xhQo

Interesting to see that he is super fast in solving the problem because he skips parsing the graph and just manually copies it into a relevant structure. Then struggles a bit to do the parsing.

https://www.youtube.com/watch?v=jMwr1Uc4g-o

Here I learned the trick to split data in two parts based on a blank line (actually to consequetive newlines)

.split('\n\n')

also learned about the pprint package and that I should definitely look into string and list indexing

[-1:] last entry
[-n:] last n entries
.extend()

Day 6

https://www.youtube.com/watch?v=LvwsB-JpJmQ

Very fast and solved this with a 3-liner. Interesting enough he solved the first problem in a very specific way and then had to generalise for the second solution. Main take away points

create the set and then check it has length n
create sets backwards to simplify range checking

if (len >= 3) and len(set(...)) == 4

Day 7

https://www.youtube.com/watch?v=ZPM5xclRInk

My approach was the same, just took me a lot longer, but I wasted time on a too complicated parser and also working around =+ operations on non-existing keys. I also used a weird logic to calculate dir names and removing the double '/' which he just ignored. Main learnings:

use defaultdict (from collections import defaultdict)
sizes = defaultdict(int)

sometimes list comprehension is not necessary

https://www.youtube.com/watch?v=YLHPABNNgZU

Also uses defaultdict and has an interesting idea to split the input on '\n$' to a single line with the command and its output.

Day 8

https://www.youtube.com/watch?v=2lypi76wRsM

This took me a long time and the above solution was both faster and more elegant. Learnings

Reading the input file directly into a useful structure as a oneliner

grid = [list( map(int, line)) for line in open(ifile).read().splitlines()]

Using all([]) returns True if all elements are True - in conjuntion with list comprehension

if all(board[r][i] < h for i in range(c)):
    return True

Use builtin functions whenever possible. In this case max() rather two-line if statement

best = max(val, best)

Day 10

Learnings:

Maybe useful to avoid multi line if

a = (A if X else B)

Initialise 2D grid

G = [['.' for _ in range(nx)] for _ in range(ny)]

Day 14

Learnings/discoveries

Use PIL for creating image

Day 21

Use 'exec' to create variables and solve by substitution

exec(f'{name} == {val}')

where name and val are previously parsed strings.

Day 24

Learned that Python's 'for' have an 'else' section

for x in s:
    if ... :
        break
else:
    didn't break

Day 25

Reversing a list

snafu[::-1]

or returning every n'the element (backwards or forwards)

a[::3]
a[::-2]

Discovered 'divmod'

q, r = divmod(8,3)

mortenjc/aoc2022