Here is my solution.

It takes less than 3 seconds on my computer.

I store the recipes in a binary, appending to it using the binary syntax. An append operation to a binary is specially optimized by Erlang’s runtime system, in that it will allocate extra storage when appending so that the next append operation will be cheaper. See the section about constructing binaries in the Efficiency Guide.

Here is my solution. It takes about 50s to finish. The long running time is because I’m dynamically building an array of about 20M elements. I resorted to using ets for this, as that works faster than using plain maps. I also briefly experimented with :array and procdict, but had no luck.

Assuming there’s no smarter algorithm, and that I didn’t make some terrible mistake, it seems that this is an example of where Erlang/Elixir are simply not performant enough. If we were able to preallocate a mutable array, this would finish much faster.

Here’s my Day 14 solution:

https://github.com/JEG2/advent_of_code_2018/blob/master/day_14/chocolate_charts.exs

I wrote pretty code then uglied it up for speed. I’m unsatisfied with where I ended up, needing about five minutes for part two.

Watch the process here (for 14 days):