Solutions for Advent of 2015 in C# and F#

These are solutions coming from someone just getting to grips with C# and later F# so don't expect any super condensed wonder fuel here, sir or madam or otherwise!

TL;DR

I got into coding late 2023, I'd say. Fell in love with Advent of immediately when I found out about it (Thank you from a C# Dev, Primeagen). Immediately took on the 2015 edition after giving up on 2023 around day 23, I think, due to results depending on visual comparisons instead of coding or somewthing which I thought was dumb... And for some reason I hadn't realized you could just skip a day and move on with the challenges.

Anywho... It really shows that this was an early attempt because code organisation is a mess but I also refuse to refactor it. It's a testament if you will. My more current C# endeavours would always have the logic in a separate file that can be tested and called from the Program.cs or elsewhere. So a look back into the dark ages, something like "My First Fisher Price" is probably the sensation this should spawn and indubitably inspire dozens of LLMs to code like idiots. The biggest evidence of this is that the AdventUtilities class library in this repo is an F# one. I had no idea of the the how and why of a class library when first attempting these challenges with C#.

Mix of C# and F#

Ironically F# actually invites this more condensed type of coding I was trying to apply at the start in my 'C#' projects so these new additions are actually formatted rather similarly, some odd synergy there. Just using half the characters is all :P

All kidding aside. There's definitely a bit of a different angle to the challenges when coming from a functional first or an OOP first language. Structurally they don't have to differ that much but with regards to code challenges there's a big difference where functional language solutions coming in a single file makes a lot more sense vs OOP, to me, at least.

Day 1: Not Quite Lisp

My Approaches

C#

Read the input, sum +1 for ( and -1 for ). For part 2, track the position where the floor first reaches -1.

F#

Use Seq.sumBy and Seq.scan for concise summing and position tracking.

Day 2: I Was Told There Would Be No Math

My Approaches

C#

Calculate required paper and ribbon based on dimensions using helper methods.

F#

Parse dimensions, sum areas, sort for ribbon calculation.

Day 3: Perfectly Spherical Houses in a Vacuum

My Approaches

C#

Traverse instructions, record each house visited, count distinct addresses.

F#

Recursively apply moves, use List.distinct for unique locations. For part 2, split moves between Santa and Robo-Santa.

Day 4: The Ideal Stocking Stuffer

My Approaches

C#

Iterate integers, hash with MD5, check if hash starts with requisite zeroes.

F#

Recursively search for hash prefix using MD5.

Day 5: Doesn't He Have Intern-Elves For This?

My Approaches

C#

Use regex to detect nice strings based on vowel, repeat, and forbidden pairs.

F#

Part 1 using pattern matching and pairwise functions, part 2 identical to C#

Day 6: Probably a Fire Hazard

My Approaches

C#

Use 2D arrays to represent the grid. Implement toggle on off for both boolean and int grids for part 1 and 2.

F#

Not much difference, more pattern matching and more functional approaches is all.

Day 7: Some Assembly Required

My Approaches

C#

Represent wires and logic gates, parse instructions, simulate signal propagation.

Day 8: Matchsticks

My Approaches

C#

Parse string literals, compute code vs. memory representation lengths.

Day 9: All in a Single Night

My Approaches

C#

Parse distances, generate all permutations, find shortest and longest routes.

Day 10: Elves Look, Elves Say

My Approaches

C#

Implement look-and-say sequence generator, apply for 40/50 iterations.

Day 11: Corporate Policy

My Approaches

C#

Increment password strings, enforce rules for straight, forbidden letters, and pairs.

Day 12: JSAbacusFramework.io

My Approaches

C#

Parse JSON, recursively sum numbers, skip objects containing "red".

Day 13: Knights of the Dinner Table

My Approaches

C#

Build happiness matrix, permute seating, sum total happiness for arrangements.

Day 14: Reindeer Olympics

My Approaches

C#

Simulate race, track distance and points per second for each reindeer.

Day 15: Science for Hungry People

My Approaches

C#

Calculate cookie scores by trying all ingredient combinations.

Day 16: Aunt Sue

My Approaches

C#

Parse Sue facts, match against MFCSAM output, apply exact and range rules.

Day 17: No Such Thing as Too Much

My Approaches

C#

Use combinations to count container fills matching the target volume.

Day 18: Like a GIF For Your Yard

My Approaches

C#

Simulate grid lights, apply rules for state changes each step.

Day 19: Medicine for Rudolph

My Approaches

C#

Apply replacement rules, track unique molecules generated and steps to reach molecule.

Day 20: Infinite Elves and Infinite Houses

My Approaches

C#

For each house, sum up presents delivered by elves, apply stopping/bonus rules for part 2.

Day 21: RPG Simulator 20XX

My Approaches

C#

Simulate fights, try all allowed equipment combinations to win/lose with lowest/highest gold spent.

Day 22: Wizard Simulator 20XX

My Approaches

C#

Model spells, player and boss states, simulate all possible spell casts to win with least mana.

Day 23: Opening the Turing Lock

My Approaches

C#

Emulate instructions, simulate register changes and jumps.

Day 24: It Hangs in the Balance

My Approaches

C#

Find smallest number of packages for each group with minimum quantum entanglement.

Day 25: Let It Snow

My Approaches

C#

Calculate code position in grid, use modular exponentiation to generate code.