Advent of Code solutions

Each day's directory contains:

1. An instruction on how to run each part of the solution (if more than 1)
2. A few sample inputs (my puzzle input is always the last one)
3. Their expected outputs.

There are also some explanations of specific functions, the approaches to the solutions, and/or ways to optimize a given solution.

Since I was learning Haskell while doing these problems, some of them are quite inefficient.