ariarule-4clojure-solution104.clj

;; ariarule's solution to Write Roman Numerals
;; https://4clojure.com/problem/104

(fn to-roman [n]
  (let [sep-rom (take-last 4 (map #(Integer/parseInt (str %)) (str "000" n)))
        rom-m (first sep-rom)
        rom-less (rest sep-rom)]
  (apply str
   (concat (repeat rom-m \M)
   (mapcat
    #(cond
      (<= %1 3) (repeat %1 %2)
      (= %1 4) (list %2 (:v %3))
      (<= %1 8) (concat (list (:v %3)) (repeat (- %1 5) %2))
      :9 (list %2 (:x %3)))
    rom-less
    '(\C \X \I)
    '({:v \D :x \M}
      {:v \L :x \C}
      {:v \V :x \X}))))))