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(require '[clojure.string :as str])
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; Build list of cave connections:
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(def caves (->> (slurp "./in")
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(str/split-lines)
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(map #(str/split % #"-"))
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(map (partial map str))
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(#(concat % (map reverse %)))
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))
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; Try to help execution speed by memoizing cave searches:
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(def search-caves
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(memoize (fn [id]
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(filter #(= (first %) id) caves))))
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; Given current path 'path', return a list of valid paths that branch
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; from 'path'. Note, paths are stored in reverse order.
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(defn get-caves-forward [path]
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(map #(cons (second %) path)
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(filter
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(fn [cv]
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(and
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; Do not return to start
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(not (str/starts-with? (second cv) "start"))
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(or
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; Always allow uppercase paths
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(< (int (first (second cv))) 96)
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(let [lw (filter #(= (str/lower-case %) %) path)]
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(or
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; Allow lowercase paths that have never been visited
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(= 0 (count (filter #(= % (second cv)) path)))
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; Allow one duplicate if there are none yet
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(= 0 (- (count lw) (count (distinct lw)))))))))
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; Only work with paths that we connect to
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(search-caves (first path))
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)))
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(loop [paths (get-caves-forward ["start"]) complete-paths []]
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(let [branches (->> paths
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(map get-caves-forward)
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(apply concat))
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complete-branches (concat complete-paths
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(filter #(= (first %) "end") branches))
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next-paths (filter #(not= (first %) "end") branches)]
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(if (empty? next-paths)
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(println (count complete-branches))
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(recur next-paths complete-branches))))
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