other-trees will be nil when there are no args to destruct there. A way to investigate things like this is to use ”inline def”.

(defn visible?
  [[tree & other-trees]]
  (def tree tree)
  (def other-trees other-trees)
  (every? #(< % tree) other-trees))

(visible? [3])

Thanks for the response. I understand other-trees will be nil, but I don't understand how it doesn't reduce to the comparison (< nil 3) and a NullPointerException, and what every? does with it.

Check out https://clojuredocs.org/clojure.core/every_q. In fact, I added a think about nil there just a few days ago, because it surprised me too.

Aha! "vacuous truth"

Yeah, ChatGPT warns about it too 😃

ChatGPT's mix of things that makes sense and pure bullshit is interesting!

Quite good except the slow performance of Java land

hehe, I don't even have eval in my implementation

not because it's hard to make, it's actually trivial, I just don't want to include it

No free will in your kingdom, @UJEK1RGJ0? 😃

it's an edn

Didn't see that one coming!

> toiling in obscurity is what you do in Java land apparently 😂

Am I the only fool staying up late to code this and document it? Oh well, so be it! Fun puzzle today. 🙂 • https://github.com/abyala/advent-2022-clojure/blob/main/docs/day09.md • https://github.com/abyala/advent-2022-clojure/blob/main/src/advent_2022_clojure/day09.clj

https://github.com/callum-oakley/advent-of-code/blob/main/src/aoc/2022/09.clj early rather than late for me! agreed this was a fun one. getting more interesting now

https://gitlab.com/maximoburrito/advent2022/-/blob/main/src/day09/main.clj No - I stayed up too. I completely misunderstood the tail following head algorithm, but what I did worked for all sample inputs and the full input on part1 but not on part 2. After re-reading for the 47th time I finally figured out what I was doing wrong. uggghh.... I applies zero cleanup here, so it's a total mess

https://github.com/nbardiuk/adventofcode/blob/master/2022/src/day09.clj

Now contains both parts. https://gist.github.com/maacl/992c94a6000ae1ae206a926eccd34294#file-clj

👋 new clojurian here. after a rough day 8, am decently pleased with my solution today. happy for any notes! https://github.com/elh/advent-2022/blob/main/src/advent_2022/day_09.clj

I reused my grid/moves->path function which takes the input and returns all coords visited, made this trivial. Each subsequent knot treats the earlier knot like the head, so iterate works nicely. Refactored with core.matrix, thanks @U02CV2P4J6S https://github.com/tschady/advent-of-code/blob/main/src/aoc/2022/d09.clj

More verbose than I would like.. but I'm not golfing after all. https://github.com/Ramblurr/advent-of-code-2022/blob/main/src/aoc/day09.clj

https://github.com/benjamin-asdf/advent-of-code/blob/master/src/Y2022/day9.clj (formatted it) feeling ultra clever today

@U02CV2P4J6S nice idea, I’m going to replace some of my vector helpers with core.matrix/{+,-} now.

had a total brain freeze for some 10 minutes trying to come up with the generalized step fn reduction https://github.com/FelipeCortez/advent-of-code/blob/master/2022/09.clj

@U01HL2S0X71 shouldn't make much of a difference here but last is linear, peek is constant https://github.com/callum-oakley/advent-of-code/blob/b562459233253a8de222e96cc17de2af6e3a040d/src/aoc/2022/09.clj#L28e

@UA2U3KW0L good catch, thanks! cuts the time almost in half 😁 (from 200ms to 100ms)

ooo, nice!

I like your move-rope implementation, @U076FM90B, since I was reducing over the indexes of my knot vector and calling update for the values in place. I think your reduce with conj of a new vector is a much cleaner solution. Once I update my blog, I think I'll be following suit!

https://github.com/alexalemi/advent/blob/main/2022/clojure/p09.clj

I took a shortcut for part 1 that slowed me down for part 2. In part one since the head only moves up down left or right, the tail, if it moves always takes the old head position. This doesn't work for part two though as intermediate knots might move diagonally.

here we go https://github.com/zelark/AoC-2022/blob/master/src/zelark/aoc_2022/day_09.clj

@U076FM90B as usual like your solution especially when it comes to moving something ^_^ btw, just checked that clojure.math has signum.

@U067R559Q cool! I've never seen it TIL. Will try to integrate into next solutions

Yikes. Wasn't sure I liked this today. Bizarrely, my solution to the second part is simpler and more general purpose (configurable numbers of knots) than my solution to the second part! One of those times knowing the second part would have helped! https://github.com/wardle/aoc2022/blob/main/src/day09.clj

Think I need to learn 'iterate' given the posted solutions above!

Didn't know the clojure.core.matrix so had to reinvent some wheels, it's not super readable though:

(defn -mapf [fc ac] (mapv #(%1 %2) fc ac))

(defn follow [H T]
  (let [diff (map - H T)]
    (if (> (apply max (map abs diff)) 1)
      (let [fx (map #(cond (> % 0) inc (< % 0) dec :else *) diff)] (-mapf fx T))
      T)))

(defn solve [input len]
  (-> (reduce
       (fn [{p :pos :as g} [m s]]
         (let [go (partial -mapf ((zipmap ["R" "L" "U" "D"] [[inc *] [dec *] [* inc] [* dec]]) m))]
           (loop [p p, n (parse-long s), g g]
             (if (zero? n) (assoc g :pos p)
                 (let [np (reduce #(conj %1 (follow (last %1) %2)) [(go (first p))] (rest p))]
                   (recur np (dec n) (update g :vis #(conj % (last np)))))))))
       {:pos (repeat len [0 0]), :vis #{[0 0]}} input)
      :vis count))

(defn -main [day]
  (let [solution (->> (file->str day) (re-seq #"\w+") (partition 2) (partial solve))]
    {:part1 (solution 2) :part2 (solution 10)}))

Day 9 https://github.com/bhauman/advent-of-code-2022/blob/main/src/adv2022/day9/sol.clj

whew, slightly ugly but here it goes:

(ns day9)

(def dirs {"U" [0 -1] "D" [0 1] "R" [1 0] "L" [-1 0]})
(def data (->> "input/day9.txt" slurp lines
               (mapcat #(let [[d n] (split % " ")] (repeat (parse-long n) (dirs d))))
               (reductions #(mapv + %1 %2) [0 0])))

(defn next-pos [[tx ty] [hx hy]]
  (let [sign (fn [x] (cond (zero? x) x (< x 0) -1 :else 1))]
    (if (or (-> tx (- hx) abs (> 1)) (-> ty (- hy) abs (> 1))) 
      [(+ tx (sign (- hx tx))) (+ ty (sign (- hy ty)))]
      [tx ty])))

(let [paths (iterate (partial reductions next-pos) data)]
  (println "1:" (->> paths second (map str) set count))
  (println "2:" (->> (nth paths 9) (map str) set count)))

Definitely need to learn how reductions work...

Me too! Great to see other people's solutions for ideas!

also, my sets don't like vectors so I had to (map str) , it wouldn't be needed in Clojure

reductions is like reduce but it returns each step

so in the case of the snake of positions you only have to keep the last position in the accumulator

Yes I see - I went through contortions to track each step in my 'reduce' which would have been unnecessary!

Yup, that would make my solution much simpler

yeah I get it, it took me a minute to see the mapping to reductions

I feel I would be cheating now to change it, but will keep in mind for coming days. That said, I am not sure I can look at my day 9 code and not change it... ! 😂

Hey if it’s in git, everyone can see the history….. so change away. That’s what I do anyway. It’s not that often that you can have this much fun coding, so I say maximize the fun and experimenting.

you know what helps? implementing the core functions as you solve

LOL

you learn a ton this way

yeah I bet

I came up with my own solution this morning, but looking over others I like some of the simpler approaches (i.e. reductions instead of loop/recur). Maybe I’ll go back and re-factor, but good enough for now. https://github.com/wevre/advent-of-code/blob/master/src/advent_of_code/2022/day_09_rope_snake.clj

An advantage to iterate/reductions is you have all this step-wise data for the visualizations that you’ll never make

Right... this is very much simpler - TIL reductions is a super power. Updated code, still can be improved but good enough. https://github.com/wardle/aoc2022/blob/main/src/day09.clj

Haha, I had just discovered reductions today also! https://github.com/leinfink/aoc-2022-clj/blob/main/src/aoc22/day9.clj

Nearly got crazy until I realised it had \d instead of \d+ in my regex so the latter parts of the input failed to parse correctly...

Reading through here, I wonder why it didn't occur to me to use reductions for the tail itself, and not just for the intermediate knots, as I did? :face_with_raised_eyebrow: Oh well, happy with my result 😇

Blergh. What an ugly solution I’ve written today. https://coyotesqrl.github.io/advent-of-code/2022/src/coyotesqrl/2022/day09.html

check if they are touching/overlap/neighbor

neighbor? (fn [xy1 xy2] (every? #{-1, 0, 1} (map - xy1 xy2)))

(->> (map - prev curr)
     (map #({2 1, -2 -1} % 0))
     (map - prev))

Happy Friday yous lot :)) I had fun taking https://github.com/mikera/core.matrix for a spin, for the first time! https://github.com/CarnunMP/Advent-of-Code/blob/master/src/y2022/d9.clj

https://clojurians.slack.com/archives/C0GLTDB2T/p1670624488987059?thread_ts=1670570395.443139&cid=C0GLTDB2T oh that could clean up my next-pos nicely, thanks Apple

@UP82LQR9N what a nice and neat solution

I thought this ended up being rather pretty

Eventually made it https://github.com/genmeblog/advent-of-code/blob/master/src/advent_of_code_2022/day09.clj

Also visualized how to knots travel. First knot and ninth knot (blues are knots from 1-8)

just for fun, rope with 100 knots 🙂

this visualization reminds me that people come up with part 3: what's the smallest number of knots such that the tail knot doesn't move https://www.reddit.com/r/adventofcode/comments/zgre9m/2022_day_9_bonus_mini_problem_only_try_after_part/

426 in my case...

very late to the game but finally got around to finishing day 09:

(ns aoc.day-09)

(let [ds    {\L [0 -1] \R [0 1] \U [-1 0] \D [1 0]}
      parse (fn [a [d n]] (concat a (repeat (parse-long n) (ds (first d)))))
      data  (reduce parse [] (partition 2 (re-seq #"\w+" (slurp "data/2022_09"))))
      head  (reductions #(mapv + %1 %2) [0 0] data)
      rope  (fn [[y x :as t] h]
              (let [[dy dx] (map - h t)
                    tx {0 0 2 1 -2 -1}]
                [(+ y (tx dy ({2 dy} (abs dx) 0))) (+ x (tx dx ({2 dx} (abs dy) 0)))]))
      tail  #(reductions rope [0 0] %)]
  (prn {:one (count (distinct (tail head)))
        :two (count (distinct (nth (iterate #(tail %) head) 9)))}))

Same here. I also made a visualization, mainly to verify my solution and because I want to get used to writing SVG. However, ran into stack overflow with the actual data, so I guess canvas would have been a better choice here. 🙂 https://github.clerk.garden/formsandlines/aoc2022-clojure/commit/a068cdff5c85be281f7bf550313d5e9a2b05d573/src/advent_of_clerk/day_09.html

Omg, reductions would have made my life so much easier (it seems like I am not the only one, looking at this thread). Also, I really like the approach of using map for simple vector math that I have seen in some solutions. I also have to remember to make more clever use of default values in collection getters.

maybe people in #C035GRLJEP8 can help. I guess there should be a way to assign custom visualiser for data based on its metadata, but I haven't looked into it.

I think Quil has been lagging way behind on jvm versions… it only works on jdk8 etc as far as I know

but if you are interested in Mathbox I can get you set up with Clerk and mathbox! https://mathbox.mentat.org/

mathbox examples: https://mathbox.org/

> I think Quil has been lagging way behind on jvm versions… it only works on jdk8 etc as far as I know Oh that's sad.. I haven't used it in quite a few years. But I thought it might be fun to use with this years AOC since there are some cool animated visualizations one can do. And since I've been using Clerk notebooks for AoC I thought it would be cool to pair them. I've also never used Quil in a web browser context, so not sure how that would work

Actually!! That might be totally fine since the cljs side uses p5.js which is up to date

Is this your code? Now you know the truth...

yes, this is my code from day 2

ChatGPT likes you! I ask it what's the date today and all I get is 'no data', 'trained till 2021'

I wonder if changing "day2" to something else would be enough to throw it off

I pasted the solution for my day 5 and asked for it to explain in human terms what it was doing. Not only did it figure out that it was an Advent of Code Day 5 solution (good namespace?) but also explained what the code was doing using words such as warehouse that weren't present in the solution. https://github.com/marceloschreiber/advent-of-code-clojure/tree/main/src/aoc/2022/day_05 (kind of hard to read)

all that while it stopped learning in 2021

I fear for my job in 5 years

not now, but 5 years is enough, maybe we should all jump on the AI train 😂

I asked chatgpt to opimtize some clojure core functions…came back with some interesting reasoning