1 files changed, 38 insertions, 0 deletions
diff --git a/year2021/day14/part2.clj b/year2021/day14/part2.clj
new file mode 100644
index 0000000..f5de5fe
--- /dev/null
+++ b/year2021/day14/part2.clj
@@ -0,0 +1,38 @@
+(require '[clojure.string :as str])
+
+(def input (->> (slurp "./in")
+                str/split-lines
+                ((juxt
+                   #(let [init-polymer (first %)]
+                      (for [i (range 0 (dec (count init-polymer)))]
+                        (subs init-polymer i (+ i 2))))
+                   (fn [lines]
+                     (->> lines
+                       (drop 2)
+                       (map #(str/split % #" -> "))
+                       (map (fn [[[a b] c]]
+                         {(str/join [a b]) (map str/join [[a c] [c b]])}))
+                       (reduce into)
+                       ))))))
+
+(def blank-map (zipmap (keys (second input)) (repeat 0)))
+
+(defn grow-polymer [polymer insertion-rules]
+  (reduce
+    #(let [[p1 p2] (insertion-rules (key %2)) v (val %2)]
+       (-> %1 (update p1 + v) (update p2 + v)))
+    blank-map
+    (filter (comp pos? val) polymer)))
+
+(def growth-seq
+  (iterate #(grow-polymer % (second input))
+           (reduce #(update %1 %2 inc) blank-map (first input))))
+
+(let [final-polymer (nth growth-seq 40) 
+      letter-counts (reduce
+                      (fn [r [k v]] (-> r (update (first k) + v) (update (second k) + v)))
+                      (zipmap (str/join (keys final-polymer)) (repeat 0))
+                      final-polymer)
+      unique-counts (filter pos? (map #(Math/ceil (/ (val %) 2)) letter-counts))]
+  (println (- (apply max unique-counts) (apply min unique-counts))))
+