AdventOfCode23

Advent of Code 2023. Solutions in Julia.

Lessons from each day

(an idea copied from Fergus's Advent of Code 2023)

• 01: Can match regular expressions.
• 02: A dictionary, Dict, was helpful.
• 03: checkbounds to check array bounds. Can use ∉ which is nice.
• 04: CSV reader has a boolean option ignorerepeated.
• 05: It can be annoying doing part A before part B - ha ha. Need to get better at using the "!" convention in function names that mutate their arguments. This one was tricky!
• 06: Shameless brute force solution as an antidote to 05. Used replace to get rid of the spaces.
• 07: Sorting.
• 08: Mapping file didn't start at AAA. lcm - yay! And falses.
• 09: pushfirst!
• 10: Part A bit more awkward than anticipated. Part B forgot to replace the starting point when looking for enclosed spaces.
• 11: reverse. count can be used to count numbers true's in an array.
• 12: Strings are immutable. Who knew? Also Threads.@threads (but don't need this with an efficient code!). Memoization. Lots to learn with this one!
• 13: transpose.
• 14: Easy to be out of phase by ±1 if not careful.
• 15: Comprehensions and generators.
• 16: count syntax for counting elements in an array that satisfy some condition.
• 17: Learn linear programming! JuMP. Tried lazy constraints which was an interesting exercise. However, redefining the nodes to have different directional states was a better approach and reduced the number of additional constraints.
• 18: Shoelace formula - wish I'd known about this before! "Obvious" result that makes the computation much easier. parse can take base argument.
• 19: eval(Meta.parse(expression)). Haven't done part B yet.
• 20: Use arrays to "allow" mutable elements in dictionary.
• 21: I wonder what part B will bring. Ug - this one is tricky! Haven't done part B yet.
• 22: Intersections.
• 23: Part A took longer than expected given that code was recycled. Part B - need to eliminate sub-tours.
• 24: Overkill for part A but thought I'd investigate how to solve a set of linear equations in Julia. SciML/LinearSolve.jl. Also for part B, NonlinearSolve.jl, even though I didn't end up using this.