Day 9 spoilers

A nice, easier day after Day 8. Code is a bit longer, but easier. Anyone who’s has to write a floodfill before got this one pretty quick.

https://github.com/massung/advent2021/blob/main/day9/day9.lisp

I fussed around a little on paper with trying to figure out how to identify local minima before realizing that it’s just a flood fill, yeah

https://github.com/benknoble/advent2021/blob/main/day9/solution.rkt Doing the fill with Qi was fun

<https://github.com/lojic/LearningRacket/blob/master/advent-of-code–2021/solutions/day09/day09.rkt|Day 9 Solution>

Nice use of remove duplicates; I was trying to come up with a better way to handle that then the typical “set of seen coordinates” approach.

Thanks. I’m relatively pleased with the code except for the repeated use of dealing with north/east/south/west coordinates.

I may create a macro for each of those, and then: (north get x y) and (north flood x y h) - not sure about that though.

Hey! This year I am trying to solve AoC problems with Racket and I have just solved day 2. Would this be the right place to ask for a code review?

Yes.

I have pushed my solution here: https://github.com/ozkutuk/aoc21/blob/master/day2.rkt

I use Haskell in my day-to-day programming and I feel like I try to use Racket pretty much the same way. I would love to learn if there are more “idiomatic Racket” alternatives to parts of my solution :smile:

@berkozkutuk since it’s late for Day 2, asking in the main channel is fine. If you start getting caught up, we have a thread for each day where people can put spoilers, so that people who haven’t coded a solution yet can avoid them :) It might help if you have specific questions re: your code review. As one comparison for day 2, here’s <https://github.com/lojic/LearningRacket/blob/master/advent-of-code–2021/solutions/day02/day02-min.rkt|my solution>

If you like haskell, you might like the qi package. It has some resemblances to point-free programming, though not entirely.

@berkozkutuk - one thing awesome about Lisp is the ability to use the reader instead of parsing and comparing. For example (Common Lisp, someone here can easily post the Racket equiv)…

(setq x 0) (defun forward (n) (incf x n)) (with-input-from-string (p "forward 10") (let ((f (read p)) (n (read p))) (funcall f n))) (print x) ; => 10

Does Racket have anything like funcall to call a function at run time by using a symbol?

#lang racket/load (define x 0) (define (forward n) (set! x (+ x n))) (with-input-from-string "forward 10" (λ () (let ([f (read)] [n (read)]) (eval (list f n))))) (print x) ; => 10

Obviously, please don’t actually do this

puzzle != production :slightly_smiling_face:

anyway, often times for these puzzles, instead of read-line, split by whitespace, etc. you can just read line then (read) all the values much easier

You can do this more sensibly with a namespace anchor.

file->list uses read to produce a list of read values, but that proc can be overwritten (so for example I have several times used a little helper called read-ignore-comma that reads the file 1,2 as the list '(1 2) rather than '(1 ,2). It does that by simply matching the result of (read) and, when it’s ,x, returning ',x , passing everything else through.). Very handy.

Day 10 spoilers

Another pretty simple day… and kinda feels like a shout-out to us lispniks, too! :wink:

https://github.com/massung/advent2021/blob/main/day10/day10.lisp