roman-numeral.clj

(ns roman-numeral)

(def number-to-roman-numeral
  [
   {:number 1000 :roman "M"}
   {:number 900 :roman "CM"}
   {:number 500 :roman "D"}
   {:number 400 :roman "CD"}
   {:number 100 :roman "C"}
   {:number 90 :roman "XC"}
   {:number 50 :roman "L"}
   {:number 40 :roman "XL"}
   {:number 10 :roman "X"}
   {:number 9 :roman "IX"}
   {:number 5 :roman "V"}
   {:number 4 :roman "IV"}
   {:number 1 :roman "I"}])


(defn to-roman-numeral
  "converts a number into its roman numeral representation"
  [number]
  (loop [currentNumber number [currentMapping & restOfMapping] number-to-roman-numeral result ""]
    (if (= currentMapping nil)
      result
      (if (>= currentNumber (:number currentMapping))
        (recur (- currentNumber (:number currentMapping)) (cons currentMapping restOfMapping) (str result (:roman currentMapping)))
        (recur currentNumber restOfMapping result)))))