AoC 2022 - Day 9

day9.clj

(ns aoc2022.day9
  (:require
   [clojure.string :as str]))

(def pos {0 0 1 1 2 1 -1 -1 -2 -1})
(def dirs {"U" [1  0] "R" [0  1] "D" [-1  0] "L" [0 -1]})
(defn move [pos move]  (mapv + pos move))
(defn diff [pos1 pos2] (mapv - pos2 pos1))
(defn touching? [d] (#{[0 1] [1 0] [1 1] [0 0]} (mapv abs d)))
(defn positions [f moves] (reductions f [0 0] moves))

(defn moves->1-step-moves
  [moves]
  (mapcat (fn [[d n]] (repeat (parse-long n) (dirs d))) moves))

(defn H-pos->T-pos
  [T-pos H-pos]
  (let [d (diff T-pos H-pos)]
    (if (touching? d)
      T-pos
      (move T-pos (mapv pos d)))))

(def common
  (->>
   (slurp "resources/input9.txt")
   str/split-lines
   (map #(str/split % #" "))
   moves->1-step-moves
   (positions move)))

(def end (comp count set))
  
;; Part 1
(->> common (positions H-pos->T-pos) end)

;; Part 2
(->> common (iterate (partial positions H-pos->T-pos)) (take 10) last end)