amalloy-4clojure-solution106.clj

;; amalloy's solution to Number Maze
;; https://4clojure.com/problem/106

(let [paths (fn [[curr :as path]]
              (for [op [* / +]
                    :let [next (op curr 2)]
                    :when (integer? next)]
                (cons next path)))
      bfs (fn [choices]
              (mapcat paths choices))]
  (fn [start end]
    (let [goal (comp #{end} first)]
      (->> [[start]]
           (iterate bfs)
           (map #(filter goal %))
           (filter seq)
           ffirst
           count))))