chrisvest-4clojure-solution75.clj

;; chrisvest's solution to http://4clojure.com/problem/75

(fn [x] (if (= x 1) 1
  (let [coprime (fn [y] (= 1
    (loop [dividend (max x y) ;; Euclid's GCD algorithm
         divisor (min x y)
         quotient (quot dividend divisor)
         remainder (rem dividend divisor)]
    (if (zero? remainder)
      divisor
      (recur divisor
             remainder
             (quot divisor remainder)
             (rem divisor remainder))))))]
    (->> (range x 0 -1) (filter coprime) count))))