Finally figured out how to write a sliding window function in J.

Code's now at https://gist.github.com/SamirTalwar/a0dddc670bda4a5cc757574bdeb5abde. I'm not uploading it to my main repo because it's not really set up to handle more than one language for the same year.

`$` is the "reshape" operator, which you can use to reshape an array.

`i. n` creates a range from 0 to n.

It works like this:

```
3 3 $ i. 9
0 1 2
3 4 5
6 7 8
```

There's gotta be a better way to create a column of numbers from 0 to n than `(n , 1) $ i. n`, but I can't find it.

Advent of Code 2021, day 2, in J.

I do not like this solution. It relies a lot on mutation and just pretending the input is J (`".` is basically `eval`).

I need to find a way to fold over my input better. Tried looking into state machines but it made my brain bleed. (https://www.jsoftware.com/help/dictionary/d332.htm)

If you need alt text, you're probably better off viewing the code at https://gist.github.com/SamirTalwar/a0dddc670bda4a5cc757574bdeb5abde.

I made my first J adverb! It takes a dyadic verb (a verb with two parameters, to its left and right), and makes the right parameter a list, which it folds over.

I feel very smug. Better go to bed before this gets out of hand.

Code here (AOC_02_2.ijs): https://gist.github.com/SamirTalwar/a0dddc670bda4a5cc757574bdeb5abde