What feels like a million years and a lifetime ago, I wrote up a library for perlin and simple noise in Racket. Inspired by Jens Axel Søgaard’s new Sketching library (processing in Racket) and a conversation thereabout, I figure it’s about time to push noise to the raco package manager!
I recently came across a question: how do you read extended file attributes in Racket. Not being actually that familiar with extended file attributes, I searched online. Nothing seems to currently exist (other than in the FUSE module, but that’s specific to FUSE), but there is a system level exectuable that one could wrap to do this. I haven’t done much1 with Racket’s system
or system*
function before, so let’s give it a whirl.
Part 1: Create an infinite stream of numbers, by starting with [3, 7] with two pointers: 0 and 1. To add values to the list:
- Add the current values of the two pointers
- If the value is less than ten, add that value to the end of the list
- If the value is greater or equal to ten, add 1 and then the ones digits to the end of the list
- Update each pointer by adding the value it is pointing at to its current index plus one
With that algorithm, find the ten digits after a given index.
Part 1: Load a minecart track that looks like this:
/->-\
| | /—-
| /-+–+-\ |
| | | | v |
-+-/ -+–/
-—–/
> Assuming minecarts follow the tracks and alternate turning left, going straight, and turning right on each intersection (`+`), where does the first collision occur?
> NOTE: Update carts top to bottom, left to right. Carts can collide mid update.
Okay. It's an interesting data format problem mostly. And we have to deal a bit with not being imperative, in particular when we're doing the updates, since having collisions happen halfway through an update is not so great. Let's load it:
```racket
(struct point (x y) #:transparent)
(struct cart (location velocity next-turn) #:transparent)
(struct track (data carts top-left bottom-right) #:transparent)
The goal will be to load the tracks into a hash of point to character (so I know how the track turns / intersects) and separately store the carts. I’ll want to process the track after the initial load to replace carts with their underlying track and get the initial velocity as well. Finally, next-turn will always start as 'left, but we’ll deal with that later.
Part 1: Create an infinite 2D cellular automaton with transition rules based on two points to each side, starting with initial state at index 0 to the right.
After 20 generations, what is the sum of indexes of points turned on?
Part 1: Define a grid as follows (x,y coordinates + a constant C):
- r(x) = x + 10
- G(x, y) = hundreds(r(x) * (r(x) * y + C)) - 5
Find the 3x3 area in a 300x300 grid with the highest total G(x, y) .
Part 1: Given a system of moving particles (with position and velocity) find the point where the particles spell a message. What is that message?
Part 1: Place marbles in a circle such that each marble is placed by skipping one place except for marbles divisible by 23. For those, don’t place them, skip back 7 places, and remove that marble as well. Add these two marbles to your current score.
Given a specific player count and last marble, what’s the highest score?
Part 1: A custom tree data structure is defined as:
- child count
- metadata count
child countadditional subtrees (recursive)metadata countmetadata nodes
Calculate the sum of all metadata nodes.
Part 1: Given a list of job dependencies (job A must be before job B), determine the order jobs must be done in. Break ties lexicographically.