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day12.clj
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day12.clj
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(ns day12
(:require [clojure.string :as str]))
(def input (slurp "input12"))
(defn map-vals [f m]
(into {}
(for [[k v] m]
[k (f v)])))
(def graph (->> input
str/split-lines
(map #(str/split % #"\-"))
(mapcat (juxt identity reverse))
(group-by first)
(map-vals (partial mapv second))))
(defn count-paths [node visited]
(if (= node "end")
1
(let [visited (cond-> visited
(not= node (str/upper-case node)) (conj node))]
(reduce +
0
(map #(count-paths % visited)
(remove visited (graph node)))))))
(count-paths "start" #{})
(defn count-paths2 [node visited allow-revisit?]
(if (= node "end")
1
(let [small? (not= node (str/upper-case node))
allow-revisit? (and allow-revisit?
(not (and small? (visited node))))
visited (cond-> visited
small? (conj node))]
(reduce +
0
(map #(count-paths2 % visited allow-revisit?)
(cond->>
(remove #{"start"} (graph node))
(not allow-revisit?) (remove visited)))))))
(count-paths2 "start" #{} true)
;; => 146553