Day 9's problem statement is convoluted - the "ah maybe that's why I don't usually do Advent of Code" kind of convoluted, but let's give it a go anyway.

So, we have a series of numbers, like so:

35
20
15
25
47
40
62
55
65
95
102
117
150
182
127
219
299
277
309
576

And uh the first N numbers are a "preamble" and every number that comes after that must be the sum of any two of the numbers that come before it.

Time for another Advent of Code 2020 problem!

That one sounds like it's going to be fun. Our input is pretty much assembly, like this:

nop +0
acc +1
jmp +4
acc +3
jmp -3
acc -99
acc +1
jmp -4
acc +6

So, the first thing we're going to do is write down some types.

There's more than one way to approach this problem, but let's go with this:

Another day, another Advent of Code 2020 problem.

That one seems fun! For some nerdy values of fun.

Our input is a set of rules:

light red bags contain 1 bright white bag, 2 muted yellow bags.
dark orange bags contain 3 bright white bags, 4 muted yellow bags.
bright white bags contain 1 shiny gold bag.
muted yellow bags contain 2 shiny gold bags, 9 faded blue bags.
shiny gold bags contain 1 dark olive bag, 2 vibrant plum bags.
dark olive bags contain 3 faded blue bags, 4 dotted black bags.
vibrant plum bags contain 5 faded blue bags, 6 dotted black bags.
faded blue bags contain no other bags.
dotted black bags contain no other bags.

The end of Advent of Code 2020 is fast approaching, and we're nowhere near done. Time to do Day 6!

The problem statement here is a little contrived, as uh, as the days that came before it, but that won't stop us.

Basically, the input looks like this:

abc

a
b
c

ab
ac

a
a
a
a

b

Each line represents one person, and "groups of persons" are separated by blank lines.

Time for another day of Advent of Code 2020.

For Day 5, we're going to have to do...

Let me guess: more parsing?

Correct!

So there's an airline that uses binary space partitioning when referring to seats - there's 128 rows and 8 columns. The first 7 characters are either F (Front, for the lower half) and B (back, for the upper half), and the last 3 are L (Left, for the lower half) or R (Right, for the upper half).

It's time for Day 4 of the Advent of Code 2020!

Now, I've already had a look at the problem statement, at least for part 1, and I'm not particularly excited.

But it will allow me to underline some of the points I've recently been *trying to make about types and correctness.

Ah, yes, the novel.

The problem is to parse passports, with fields like these:

Hello all, and welcome back to Advent of Code 2020, featuring Cool Bear.

Hey y'all!

Let's get right to it.

The problem statement for Day 3 is as follows: we're given a map, that looks like this:

..##.......
#...#...#..
.#....#..#.
..#.#...#.#
.#...##..#.
..#.##.....
.#.#.#....#
.#........#
#.##...#...
#...##....#
.#..#...#.#

And we that it repeats infinitely to the right, like so:

Day 2, Day 2! Woo!

The Advent of Code 2020, Day 2 problem talks about passwords. Sounds familiar.

Basically, our input looks like this:

1-3 a: abcde
1-3 b: cdefg
2-9 c: ccccccccc

Each line contains a "password policy" and a "password". For the first line, the policy is that the password must contain between 1 and 3 (inclusive) times the letter "a".