Advent of Code 2020 Solutions

Various solutions to the 2020 problems. Golf style!

Background

Original solutions were written as "oneliners" with a custom build of the hoe tool, as well as several solutions in perl and j. You can find these solutions in the ./oneliners/ directory of this project. Since this makes it difficult to run them yourself, I've created a cabal project to explicitly list all the dependencies, etc.

Source

Source for solutions is found in src/. With part one and two located in the same AdventDAY.hs file.

Running

All solutions are run by calling cabal run advent2020 DAY[b].

Input is provided on STDIN except in a few cases indicated by the lack of interact in Main.hs.

Example: cabal run advent2020 22b < advent22.input.

Favourite Solutions

Day 6: Plane Seating - Binary Interpretation
Day 17: Conway Cubes - List Comprenensions to the Rescue
Day 19b: Parser Builder with Non-Determinism
Day 24: Hexagon Grid - Coordinate transformation problem solved with Ren

Solutions of Interest - Line Notes

Day 1: Simple use of list-comprehensions.
Day 2: Use of lens regex library.
Day 3: Tabulated functions.
Day 6: Direct binary interpretation.
Day 7: Regexes with groups.
Day 7: Use of Zoom from Lens.
Day 10: Dynamic programming solution using Arrays for subsolutions.
Day 12: Heavy use of stateful lenses. Tabulated functions.
Day 13: Chinese remainder theoreb using arithmoi library. Needed a hint as I could only figure out that I needed the extended Euclid algorithm to solve this but went down a rabbit hole of Galois theory which wasn't required.
Day 14: More stateful lenses.
Day 17: Conway Cubes: More list comprehensions
Day 18: Terrible handrolled parser for part 1. Parsec based operator parsers with associativity for part 2.
Day 19: More parsing. Dynamic parser assembly. Nondeterministic parsing for Part 2. Most elegant solution!
Day 20: Tile assembly. Was difficult to get right.
Day 22: Card game - Very concise solution for part 1. Use of Sets for part 2 to speed it up.
Day 23: Cup game - Simple solution for part 1. Very slow for part 2 - Had to find a hint and used a mutable "following cup index array" trick.
Day 24: Hexagon grid - Main trick was translating "3d" hex coords to "2d" hex coords.
Day 25: Just used a brute force translation of the algorithm description. Hoped to spot an obvious number-theory approach that would solve this instantly, but nothing came to mind.

General Observations

Missing fixf function from stdlib.

sordina / advent2020