digits.clj

;;; Import functions from one of my own modules
;;; I think I need to understand/set up CLASSPATH

(ns digits)

(def digit_map
     { \0 0 \1 1 \2 2 \3 3 \4 4 \5 5 \6 6 \7 7 \8 8 \9 9 })

(defn digits-1
  "Return the digits of a number as a list"
  [number]
  (map #(- (int %) (int \0)) (seq (str number))))

(defn digits-2
  "Return the digits of a number as a list"
  [number]
  (let [m { \0 0 \1 1 \2 2 \3 3 \4 4 \5 5 \6 6 \7 7 \8 8 \9 9 }]
    (map #(m %) (seq (str number)))))

(defn digits-3
  "Return the digits of a number as a list"
  [number]
  (reverse (map #(rem % 10) (take-while #(> % 0) (iterate #(quot % 10) number)))))

(defn digits-4
  "Return the digits of a number as a list"
  [number]
  (map #(digit_map %) (seq (str number))))

;;; now let's see which is fastest ...
(time (dotimes [_ 100000] (digits/digits-1 1234)))
(time (dotimes [_ 100000] (digits/digits-2 1234)))
(time (dotimes [_ 100000] (digits/digits-3 1234)))
(time (dotimes [_ 100000] (digits/digits-4 1234)))

;; "Elapsed time: 58.449 msecs"
;; "Elapsed time: 265.609 msecs"
;; "Elapsed time: 907.47 msecs"
;; "Elapsed time: 57.948 msecs"

(println "so 1 and 4 are fastest, let's give em longer strings ...")
(time (dotimes [_ 100000] (digits/digits-1 1234567890)))
(time (dotimes [_ 100000] (digits/digits-4 1234567890)))

;; "Elapsed time: 67.175 msecs"
;; "Elapsed time: 67.576 msecs"
(println "so it seems 1 is better for longer strings, therefore 1 is the winner ;)")