From 5ff78d12414b9c756fab419896cbc4d561188080 Mon Sep 17 00:00:00 2001
From: Leah Neukirchen <leah@vuxu.org>
Date: Sun, 12 Dec 2021 01:50:27 +0100
Subject: day11

---
 day11     | 10 ++++++++++
 day11.bqn | 14 ++++++++++++++
 day11.clj | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)
 create mode 100644 day11
 create mode 100644 day11.bqn
 create mode 100644 day11.clj

diff --git a/day11 b/day11
new file mode 100644
index 0000000..95f25a9
--- /dev/null
+++ b/day11
@@ -0,0 +1,10 @@
+4781623888
+1784156114
+3265645122
+4371551414
+3377154886
+7882314455
+6421348681
+7175424287
+5488242184
+2448568261
diff --git a/day11.bqn b/day11.bqn
new file mode 100644
index 0000000..03d4dcd
--- /dev/null
+++ b/day11.bqn
@@ -0,0 +1,14 @@
+While ← {𝕩{𝔽⍟𝔾∘𝔽_𝕣_𝔾∘𝔽⍟𝔾𝕩}𝕨@}´
+d←>'0'-˜•FLines"day11"
+
+Step ← {
+  g←f←0× x←𝕩+1
+  While {𝕤 ⋄ f ≢ f ∨ g ↩ (¬f) ∧ x>9 }‿{𝕤
+    x +↩ (+´+˝)⎉2 3‿3↕{⌽⍉0∾˘𝕩}⍟4 g
+    f ∨↩ g
+  }
+  x × ¬f∨g
+}
+
+•Out +´{+´⥊0=𝕩}¨ Step⍟(↕101) d
+•Out 0 {∧´0=⥊𝕩 ? 𝕨 ; (𝕨+1) 𝕊 Step 𝕩} d
diff --git a/day11.clj b/day11.clj
new file mode 100644
index 0000000..0b34170
--- /dev/null
+++ b/day11.clj
@@ -0,0 +1,51 @@
+(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
-- 
cgit 1.4.1