In the day 8 problem, our input is a height map:

30373
25512
65332
33549
35390

This is a 5x5 grid, and every number denotes the height of a tree. For part 1, we must find out how many trees are visible from the outside of the grid.

If we consider the first row, from the left: only the 3 is visible: it obscures the 0. From the right, 3 and 7 are visible.

Two years ago, I did part of Advent of Code 2020 using the Rust language. It was a lot of fun, so let's try it again!

Our input looks something like this:

1000
2000
3000

4000

5000
6000

7000
8000
9000

10000

Each group of lines separated by an empty line is a list of food items an elf is carrying: each line corresponds to the number of calories in that food.