「ClojureでNinety-Nine Lisp Problems(P31～33)」ブログ用

p31.clj

(defn my-prime?
  "Determine whether a given integer number is prime."
  ([n]
    (cond
      (<= n 1) false
      (== n 2) true
      (== (rem n 2) 0) false
      (some #(== (rem n %) 0) (range 3 (inc (Math/sqrt n)) 2)) false
      :else true)))

p32-1.clj

(defn my-gcd
  "Determine the greatest common divisor of two positive integer numbers."
  [n m]
  (cond
    (== n 0) m
    (neg? n) (my-gcd (- n) m)
    (neg? m) (- (my-gcd n (- m)))
    :else (my-gcd (rem m n) n)))

p32-2.clj

(defn my-gcd
  "Determine the greatest common divisor of two positive integer numbers."
  [n m]
  (cond
    (== n 0) (Math/abs m)
    (== m 0) (Math/abs n)
    :else (let [ns (range (quot (max (Math/abs n) (Math/abs m)) 2) 0 -1)]
            (some #(if (and (== (rem n %) 0) (== (rem m %) 0)) %) ns))))

p33.clj

(declare my-gcd)

(defn my-coprime?
  "Determine whether two positive integer numbers are coprime."
  [n m]
  (let [g (my-gcd n m)] (or (== g 1) (== g -1))))

(defn my-gcd
  "Determine the greatest common divisor of two positive integer numbers."
  [n m]
  (cond
    (== n 0) m
    (neg? n) (my-gcd (- n) m)
    (neg? m) (- (my-gcd n (- m)))
    :else (my-gcd (rem m n) n)))