(ns untitled2.core)

(defn gen_seq
  [prefix, alphabet]
  (->> alphabet
       (filter (fn [x] (not= x (str (last prefix)))))
       (map (fn [x] (concat prefix x)))))

(defn gen_seq_for_prefixes
  [prefixes, alphabet]
  (reduce
    (fn [memo, prefix] (concat memo (gen_seq prefix alphabet)))
    []
    prefixes))

(defn -main
  []
  (let [input ["a" "b" "c"] N 2]
    (println
      (map
        (fn [seq] (apply str seq))
        (reduce
          (fn [memo, _] (gen_seq_for_prefixes memo input))
          input
          (take N (range)))))))