Oh! I almost forgot it is worth mentioning the creator of Elixir Language "José Valim" also solves these problems and streams them on twitch [0].

Those are helpful to learn different approaches to solving these problems.

[0] Github: https://github.com/josevalim/aoc

[1] Twitch: https://www.twitch.tv/collections/k_DLnk2tvBa-fQ