Advent of Code Kotlin Template

Advent of Code – an annual event in December since 2015. Every year since then, with the first day of December, a programming puzzles contest is published every day for twenty-four days. A set of Christmas-oriented challenges provide any input you have to use to answer using the language of your choice. We offer you a template prepared to use with Kotlin language within this repository.

Workflow

Advent of Code Kotlin Template is a particular type of GitHub repository that lets you speed up the setup phase and start writing your AoC solutions immediately.

The general idea is straightforward – to create a new project based on this template, you need to log in to your GitHub account and use the Use this template green button. And remember – do not fork it!

After creating a new project based on this template in your account, a dedicated GitHub Actions workflow will start and clean up the code from redundant files. It will also personalize code to use your username and project name in namespaces and Gradle properties. How cool is that?

Right after the @actions-user actor pushes the second commit to your repository, you're ready to clone it within the IntelliJ IDEA.

From now, everything's in your hands! Join the Advent of Code contest, solve the Day O1 as soon as it is published.

For the following days, copy the Day01.kt solution file and increment the day number.

Remember to join the Kotlin contest!

To do that, edit your project's About section with ⚙️ icon and add the aoc-2021-in-kotlin topic to your project.

We will find your repository and count you in our giveaway.

Content

After you create a new project based on the current template repository using the Use this template button, a bare minimal scaffold will appear in your GitHub account with the following structure:

.
├── README.md               README file
├── build.gradle.kts        Gradle configuration created with Kotlin DSL
├── gradle
│   └── wrapper             Gradle Wrapper
├── gradle.properties       Gradle configuration properties
├── gradlew                 *nix Gradle Wrapper script
├── gradlew.bat             Windows Gradle Wrapper script
├── settings.gradle.kts     Gradle project settings
└── src
    ├── Day01.kt            An empty implementation for the first AoC day
    ├── Day01.txt           An empty file for the Day 01 input data
    ├── Day01_test.txt      An optional Day 01 test input data used for checks
    └── Utils.kt            A set of utility methods shared across your days

Note: All task input files are excluded from the repository with .gitignore – we should not post them publicly, as Eric Wastl asks for: Tweet.

When the first puzzle appears, go to the Day01.kt and for each part1 and part2 functions, provide an algorithm implementation using the input data loaded from the src/Day01.txt file. This input data is common for both parts, and you can find it on the bottom of each day on the Advent of Code page.

To read the input data, you can go with the readInput(name: String) utility method provided in the Utils.kt file, like:

fun main() {
    fun part1(input: List<String>): Int {
        return input.size
    }

    val input = readInput("Day01")
    println(part1(input))
}

The Utils.kt file also contains the String.md5() method for generating MD5 hash out of the given string and expects more helper functions for the sake of the KISS principle.

Each puzzle describes some test conditions, a small portion of the information that helps check if the produced value for the given test input is valid. To handle that case, you can put such an input into a separated file and perform a check against the output, like:

fun main() {
    // ...
    
    val testInput = readInput("Day01_test")
    check(part1(testInput) == 13)
}

The current approach of providing both part1 and part2 solutions within the single Day##.kt file may sometimes bring a disadvantage due to the first solution calculation when we expect to work on the second part only. With simple cases that don't consume too much of your time and resources that can be almost unnoticeable, but when solution takes seconds, it is worth considering breaking daily solution into two separated pieces, like Day07_part1.kt and Day07_part2.kt.

The final result of your algorithm will be printed on the screen so that you can pass it to the Advent of Code website.

To go with the next day, place the Day02.txt file into the src with relevant input data and create Day02.kt file with a similar code scaffold:

fun main() {
    fun part1(input: List<String>): Int {
        return 0
    }

    fun part2(input: List<String>): Int {
        return 0
    }

    val input = readInput("Day02")
    println(part1(input))
    println(part2(input))
}

Getting help

If you stuck with Kotlin-specific questions or anything related to this template, check out the following resources:

• Kotlin docs
• Kotlin Slack
• Template issue tracker