Advent of Code 2019

Solutions by Alexey Filippov

This repository is for solutions for Advent of Code 2019 by me. The code you see is not necessarily the code that produced the submitted result - as I go and re-use the earlier code, I refactor it as I see fit. I cannot promise that everything works, either - going back and forth is time consuming, so if you want to see that code that did run, search for the version on the day the task was published - it's likely to be the best version, as it avoided the second-system effects.

I do not claim full ownership of the solutions' code. For example, the brilliant pairs = zip <*> tail hack is taken from StackOverflow; when I'm struggling to find a proper import (e.g. day 4), I copy Haskell library functions from Hoogle/Hackage.

This repository is merely a scratch pad for me to look up the tasks I can build upon.

1. Simple exercise on iterate - add fuel until enough to carry itself
2. A simple runtime for "Intcode" machine: add and mul for now, indirect addressing
3. Search for intersection of wires, two definitions of distance
4. Patterns in numbers' decimary representation. Run-length encoding
5. Add jit, jif, in and out instructions for Intcode interpreter
6. Distances over tree - sum of all distances from a point, shortest distance in an ordered tree
7. Run Intcode until blocking output, encapsulate the run
8. A general task, speed coding chunkOf n and reduce/foldl
9. Full Intcode computer with relative address mode
10. Computational geometry, visibility on a grid, coordinates to angles
11. Interacting states; I need more practice with monad transformers
12. 4-body problem in 3D. Part 1 is straightforward coding, part 2 is a single-insight puzzle