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(require '[clojure.string :as str])
(def input (->> (slurp "./in2")
str/split-lines
((juxt
first
(fn [lines]
(->> lines
(drop 2)
(map #(str/split % #" -> "))
(flatten)
(apply (partial assoc {}))
))))))
(def blank-map
(reduce
#(assoc %1 %2 0)
{}
(keys (second input))))
(defn grow-polymer [polymer insertion-rules]
(reduce
(fn [res pair]
(let [pk (key pair)
p1 (str/join [(first pk) (insertion-rules pk)])
p2 (str/join [(insertion-rules pk) (second pk)])]
(-> res (update p1 + (val pair)) (update p2 + (val pair)))
))
blank-map
(filter #(pos? (val %)) polymer)
))
(def growth-seq
(iterate
#(grow-polymer % (second input))
(reduce
#(update %1 %2 inc)
blank-map
(for [i (range 0 (dec (count (first input))))]
(subs (first input) i (+ i 2))))))
(let [results
(map #(Math/ceil (/ % 2))
(vals
(reduce
(fn [r p] (-> r
(update (first (key p)) #(if (nil? %) (val p) (+ % (val p))))
(update (second (key p)) #(if (nil? %) (val p) (+ % (val p))))))
{}
(nth growth-seq 40))))]
(println (- (apply max results) (apply min results))))
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