by Kristian Rother

This cheat sheet was originally prepared for a talk at PyLadies Hamburg.

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Advent of Code is an advanced coding challenge.

• one challenge released at 5:00 a.m. UTC per day December 1st - 25th
• every challenge has two parts
• there are >100k participants globally
• collect up to 50 stars (two per day)
• the challenges come with great santa stories

• rehearse coding fundamentals
• understand requirements
• decompose problems into smaller parts
• estimate computational complexity
• programming practices (OOP, functional programming)
• code cleanup, refactoring

The biggest step towards the solution is choosing a good data structure. All problems can be solved with standard Python data types: list, dict, set

Data structures that you will need for some of the challenges are:

• stack
• queue
• chained list
• tree
• graph
• 2D array

Identifying a good algorithm is essential. For many challenges a brute-force solution is computationally infeasible!

Here are some algorithms that I have used in AoC with links to according challenges:

• Move along a 2D grid
• Crypto mining
• Graph traversal
• Interpreting an assembly-like language
• Conways Game of Life
• Josephus Problem
• Dynamic Programming (backpack)
• 2D Convolutional Kernel
• kd-Tree
• Dijkstra

Most challenges use strings and integer numbers only. You do not have to worry about floating-point precision, probabilities and heuristic algorithms.

To learn more about algorithmics, I recommend Algorithms by Robert Sedgewick and Kevin Wayne.

Some Python libraries I have used over and over in AoC:

• re– essential to parse most inputs
• numpy – fast arrays help with many challenges
• deque – fast queue implementation (much faster than list)
• heapq – for priority queues
• itertools – iterable helpers like permutations, products etc.

Careful with deepcopy (slow)

I made heavy use of automated tests using pytest:

• test a minimal input first
• copy-paste the small examples from the AoC page, write tests for them
• test your toplevel functions only unless it gets really difficult
• add more examples to cover boarder cases (use @pytest.mark.parametrize)
• great opportunity to exercise TDD (see live TDD in Uncle Bobs "Clean Code" lecture

AoC works great in teams with:

• pair programming
• people using different programming languages
• beginners who spend their time researching stuff
• solving challenges of a previous year at a slower pace

Doing this for 25 days in a row is physically and mentally exhausting! You can hurt yourself!

A better idea might be

• Go slow and steady.
• Do not try to go as fast as possible.
• Do lots of refactoring and code cleanup
• It is OK to stop at any point.
• If you solve one problem, be proud of yourself already.

You can find my solutions on www.github.com/krother/advent_of_code.

(c) 2022 Dr. Kristian Rother

This Cheat Sheet is available under the conditions of the Creative Commons Attribution International License 4.0

The code on www.github.com/krother/advent_of_code is available under the conditions of the MIT License. See LICENSE.TXT for details.