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(require '[clojure.string :as str])
; The given program operates on a base-26 stack, either pushing or
; (conditionally) popping values. This code extracts those operations
; from the input, then works through them to determine the highest
; and lowest values that produce an output of zero.
; See the .md file in this directory for more info.
(def program (->> (slurp "./in")
str/split-lines
(map #(str/split % #"\s+"))
(partition 18)
(map (fn [step]
(if (= "1" (last (nth step 4)))
[:push (read-string (last (nth step 15)))]
[:pop (read-string (last (nth step 5)))])
))))
(defn program-index [prog] (- 14 (count prog)))
(loop [numbers (vec (repeat 2 (vec (repeat 14 0))))
stack '()
prog program]
(if-let [step (first prog)]
(if (= :push (first step))
(recur numbers
(conj stack [(program-index prog) (second step)])
(rest prog))
(let [i2 (program-index prog)
[i1 v] (first stack)
diff (+ v (second step))]
(recur
[(if (neg? diff)
(-> (first numbers) (assoc i1 9) (assoc i2 (+ 9 diff)))
(-> (first numbers) (assoc i2 9) (assoc i1 (- 9 diff))))
(if (neg? diff)
(-> (second numbers) (assoc i2 1) (assoc i1 (- 1 diff)))
(-> (second numbers) (assoc i1 1) (assoc i2 (+ 1 diff))))]
(rest stack) (rest prog))))
(println (map str/join numbers))))
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