euler38.clj

euler38.clj

(defn split [n]
  (cond
    (< n 10) [n]
    :else (conj
      (split (quot n 10))
      (rem n 10))))

(defn join [numbers]
  (reduce
    #(+ (* 10 %1) %2)
    (reduce into (map split numbers))))

(defn check [pan n]
  (loop [pan (split pan), i 1]
    (let [n (* n i), nsp (split n), size (count nsp)]
      (cond
        (= nsp pan) true
        (= nsp (take size pan)) (recur (drop size pan) (inc i))
        :else false))))

(defn from-concat? [pan]
  (some
    (partial check pan)
    (for [i (range 1 6)] (->> pan split (take i) join))))


(use 'clojure.contrib.combinatorics)
(def pans (permutations [9 8 7 6 5 4 3 2 1]))
(prn (join (first (filter #(from-concat? (join %)) pans))))