divmod.clj

(ns divmod.core)

; division by repeated subtraction
; http://en.wikipedia.org/wiki/Division_algorithm#Division_by_repeated_subtraction

(defn divmod
  [n d]
  (cond
    (= d 0) (throw (Throwable. "Division By Zero"))
    (< d 0)
      (let [[q r] (divmod n (- d))]
        [(- q) r])
    (< n 0)
      (let [[q r] (divmod (- n) d)]
        (if (= r 0)
          [(- q) 0])
          [(dec (- q)) (- d r)])
    :else
      (loop [q 0
             r n]
        (if (< r d)
          [q r]
          (recur (inc q) (- r d))))))

; (use 'divmod.core :reload)

; (divmod 1 1)
;=> [1 0]

; (divmod 1 2)
;=> [0 1]

; (divmod 20 5)
;=> [4 0]

; (divmod 5 20)
; [0 5]

; (divmod 5 4)
;=> [1 1]

; (divmod 1000000 0)
;=> #<Throwable java.lang.Throwable: Division By Zero>