Advent of Code 2021 Solutions

This repo contains my Advent of Code 2021 solutions in Java 17. After providing it with your puzzle inputs (or your session token), running the program will print out the answers to all days of the puzzle. A Docker image is provided to ensure compatibility with machines that do not want to install the Java 17 runtime.

The goal of this repo is to provide fast, highly tested, and easy-to-use solutions. When run on my PC (an AMD Ryzen 9 3950X), all answers are outputed in ~2.6 seconds. OCR is also automatically performed for Day 13's puzzle to avoid requiring interpretation.

This repo may see changes in the future to improve runtime. If you have any suggestions, issues running the code, or find a correctness error: please open an issue or pull request.

Example output:

Day 01 Part 1: 1532
Day 01 Part 2: 1571
Day 02 Part 1: 1604850
Day 02 Part 2: 1685186100
Day 03 Part 1: 3885894
Day 03 Part 2: 4375225
Day 04 Part 1: 87456
Day 04 Part 2: 15561
Day 05 Part 1: 6113
Day 05 Part 2: 20373
Day 06 Part 1: 349549
Day 06 Part 2: 1589590444365
Day 07 Part 1: 356922
Day 07 Part 2: 100347031
Day 08 Part 1: 318
Day 08 Part 2: 996280
Day 09 Part 1: 550
Day 09 Part 2: 1100682
Day 10 Part 1: 271245
Day 10 Part 2: 1685293086
Day 11 Part 1: 1634
Day 11 Part 2: 210
Day 12 Part 1: 4338
Day 12 Part 2: 114189
Day 13 Part 1: 655
Day 13 Part 2: JPZCUAUR
Day 14 Part 1: 3247
Day 14 Part 2: 4110568157153
Day 15 Part 1: 458
Day 15 Part 2: 2800
Day 16 Part 1: 883
Day 16 Part 2: 1675198555015
Day 17 Part 1: 7626
Day 17 Part 2: 2032
Day 18 Part 1: 4323
Day 18 Part 2: 4749
Day 19 Part 1: 308
Day 19 Part 2: 12124
Day 20 Part 1: 5597
Day 20 Part 2: 18723
Day 21 Part 1: 504972
Day 21 Part 2: 446968027750017
Day 22 Part 1: 615700
Day 22 Part 2: 1236463892941356
Day 23 Part 1: 18282
Day 23 Part 2: 50132
Day 24 Part 1: 91398299697996
Day 24 Part 2: 41171183141291
Day 25 Part 1: 300
Day 25 Part 2: Day 25 has no part 2

Providing Your Puzzle Input

There are two supported methods for inputting your puzzle data into this application.

Automatic Puzzle Fetcher (via Session Cookie)

First, get your cookie session data.

You will need to log into the Advent of Code website and then inspect your cookies. If you are using Chrome, you can follow the directions here.

You will be looking for a cookie called session. It will contain a long sequence of hexadecimal digits.

Place that data into a file called cookie.txt in the project directory.

The application will use that data to automatically fetch your puzzle input for each day.

Manual Input

This code will also look in a particular location on your local machine for puzzle input.

In the project directory, it will check a directory called puzzle. Within that directory it will expect Day 1's input to be in a file called 1, Day 2's input to be in a file called 2, etc.

You can find your puzzle input for a given day by logging into the Advent of Code website and then navigating to the URL for that puzzle's input.

The URL for your puzzle input will be at:

https://adventofcode.com/2021/day/${DAY}/input

where ${DAY} is the day number of the puzzle.

As an example, Day 1's input is at https://adventofcode.com/2021/day/1/input, Day 2's input is at https://adventofcode.com/2021/day/2/input, etc.

Docker Instructions (Mac/Linux)

1. Follow the instructions above for providing your puzzle input.
2. Run docker run --rm -it $(docker build -q .)

Windows Instructions

1. Follow the instructions above for providing your puzzle input.
2. Install JDK 17. You can follow the installation instructions here.
3. Open a command prompt and navigate to the project directory.
4. Run .\gradlew.bat run

Mac Instructions

1. Follow the instructions above for providing your puzzle input.
2. Install JDK 17. You can follow the installation instructions here.
3. Open Terminal and navigate to the project directory.
4. Run ./gradlew run

Linux Instructions

1. Follow the instructions above for providing your puzzle input.
2. Install JDK 17. You can follow the generic installation instructions here. Alternatively, you may want to search on Google for installation instructions specific to your distro.
3. Open a shell and navigate to the project directory.
4. Run ./gradlew run