Last year I attempted it during a comically short time (only 3 days), but was able to settle on something like this: https://github.com/j1elo/advent-of-code-2018-rust/blob/maste...

i.e. pass the input from standard input, and just build an on-the-go Vector of some data type that is appropriate for the problem at hand. Day 3 was different from 1 and 2 in that for the first time the parsing was not immediate; using Serde and Recap modules did a fantastically succinct job of parsing the text input. Of course it depends on how much you want to rely on external crates.

Let's see if this year I can do more than 3 days worth of AoC :-)