🎄🎁🎅 2021 Advent of Code in Kotlin 🎅🎁🎄

Project goals

The project goal is to deliver some pretty, readable and concise solutions to Advent of Code 2021 problems all written in Kotlin language. It should show the other developer how some constructions from the language can be used and how to solve some kind of tricky problems that appear during the Advent of Code.

Problems source

You can find all problems at the page of Advent of Code 2021. The description of each problem contains some sample test data, but I also included my input data files from the contest in the resources' directory of the project to make my project working with some sample, real world data.

Solution template

When soling each day problem I use my template of AdventDay that I defined in AdventDay.kt - it's worth looking into this definition by yourself, and also you can read more about it at my blog.

It's enough to create some Kotlin object that inherits from AdventDay to get the solution running. If you're interested in the details, let's look into the definition of the Advent.kt to see how to find all object classes in Kotlin and run some method on them 😎.

To run all solutions, simply call ./gradlew run

Tests

The solutions are tested with the values gathered from adventofcode.com. Every day of Advent has its expected output defined in AdventTest.kt and in order to verify correct state of the outputs for days we run every day solution and catch it standard output stream to compare it with expected value.

To run all tests, simply call ./gradlew test

Problems

The problems solutions are included in project, but for every of them you can also find some corresponding article at my website, where I discuss not only the given problem, but also some cool features of Kotlin or I deep dive into some language constructions.

Problem	Solution	Blog Post	Tags
Day 1: Sonar Sweep	Day1.kt	Day 1 Blog Post	Sequence<T>, windowed
Day 2: Dive!	Day2.kt	Day 2 Blog Post	fold, inline, takeIf
Day 3: Binary Diagnostic	Day3.kt	Day 3 Blog Post	readable, abstracted
Day 4: Giant Squid	Day4.kt	Day 4 Blog Post	groupDividedBy, transpose, context
Day 5: Hydrothermal Venture	Day5.kt	Day 5 Blog Post	DefaultMap<K, V>, directedTo, IntProgression
Day 6: Lanternfish	Day6.kt	Day 6 Blog Post	crossinline, data structures
Day 7: The Treachery of Whales	Day7.kt	Day 7 Blog Post	median, average, math, named args
Day 8: Seven Segment Search	Day8.kt	Day 8 Blog Post	operator fun, deduction
Day 9: Smoke Basin	Day9.kt	Day 9 Blog Post	operator fun, tailrec fun, dfs, bfs
Day 10: Syntax Scoring	Day10.kt	Day 10 Blog Post	foldRight, Stack<V>, bracket pairing
Day 11: Dumbo Octopus	Day11.kt	Day 11 Blog Post	Sequence<T>, operator fun set, operator fun get, LazyDefaultMap<K, V>
Day 12: Passage Pathing	Day12.kt	Day 12 Blog Post	@JvmInline, value class, dfs, paths in graph
Day 13: Transparent Origami	Day13.kt	Day 13 Blog Post	fold, immutable data, reflections, origami
Day 14: Extended Polymerization	Day14.kt	Day 14 Blog Post	immutable data, data structure, buildMap { }, operator fun invoke
Day 15: Chiton	Day15.kt	Day 15 Blog Post	weighted graph, dijkstra, shortest path
Day 16: Packet Decoder	Day16.kt	Day 16 Blog Post	by notNull(), delegated properties, Sequence<T>, date parsing
Day 17: Trick Shot	Day17.kt	Day 17 Blog Post	simulation, physics, immutable data
Day 18: Snailfish	Day18.kt	Day 18 Blog Post	tree, reduce, traversal, lateinit var
Day 19: Beacon Scanner	Day19.kt	Day 19 Blog Post	3D rotation, matching, infix fun, named block
Day 20: Trench Map	Day20.kt	Day 20 Blog Post	infix fun, operator fun, extension properties, IntRange
Day 21: Dirac Dice	Day21.kt	Day 21 Blog Post	simulate, immutable data, DefaultMap<K, V>, counting, fold, generateSequence
Day 22: Reactor Reboot	Day22.kt	Day 22 Blog Post	IntRange, Range3D, infix fun, operator fun
Day 23: Amphipod	Day23.kt	Day 23 Blog Post	HashSet, simulation, memorization, Dijkstra, data class
Day 24: Arithmetic Logic Unit	Day24.kt	Day 24 Blog Post	ALU, reverse engineering, interpreter, sealed interface vs enum class
Day 25: Sea Cucumber	Day25.kt	Day 25 Blog Post	immutable data class, function receiver, Sequence<T>