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