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(ns org.vuxu.aoc2021.day11
(:require [clojure.string :as str]
[clojure.set :as set]))
;; attribution: https://www.reddit.com/r/adventofcode/comments/rds32p/2021_day_11_solutions/ho4d867/
(defn parse-digit [char]
(Character/digit char 10))
(def data
(->> (slurp "day11")
(str/split-lines)
(mapv (partial mapv parse-digit))))
(def datamap
(zipmap (for [x (range (count data))
y (range (count (data x)))]
[x y])
(flatten data)))
(defn neighbours [[x y]]
(for [dx [-1 0 1]
dy [-1 0 1]
:when (< -1 (+ x dx) (count data))
:when (< -1 (+ y dy) (count (first data)))]
[(+ x dx) (+ y dy)]))
(defn trigger [flashed grid]
(let [flashing (set/difference
(set (map first (filter (fn [[k v]] (> v 9)) grid)))
flashed)
new-grid (reduce (fn [g p] (update g p inc))
grid
(mapcat neighbours flashing))]
(if (empty? flashing)
[flashed grid]
(trigger (set/union flashed flashing) new-grid))))
(defn step [[_ grid]]
(let [[flashed updated] (trigger #{} (update-vals grid inc))]
[(count flashed)
(apply merge updated (map #(vector % 0) flashed))]))
(def part1
(apply + (take 101 (map first (iterate step [0 datamap])))))
;; => 1713
(def part2
(count (take-while #(< % (* (count data) (count (first data))))
(map first (iterate step [0 datamap])))))
;; => 502
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