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