「ClojureでNinety-Nine Lisp Problems(P40, 41)」ブログ用

p40.clj

(declare my-primes)

(defn my-goldbach
  "Goldbach's conjecture."
  [n]
  (if (or (odd? n) (== n 2))
    nil
    (loop [ps (my-primes n)]
      (let [[p' & ps'] ps, m (first (drop-while #(> n (+ % p')) ps))]
        (if (and (not (nil? m)) (== (+ p' m) n))
          (list p' m)
          (recur ps'))))))

(defn my-primes
  [n]
  (loop [n n, [m & ms] (cons 2 (iterate #(+ 2 %) 3)), ps nil]
    (if (> m n)
      (reverse ps)
      (let [ps' (drop-while #(> (Math/pow % 2) m) ps),
            ps'' (if (every? #(not= (rem m %) 0) ps') (cons m ps) ps)]
        (recur n ms ps'')))))

p41.clj

(declare my-primes my-goldbach)

(defn my-goldbach-list
  "A list of Goldbach compositions."
  ([n m]
    (my-goldbach-list n m 0))
  ([n m l]
    (filter (fn [[_ g]] (and (not (nil? g)) (>= (first g) l)))
      (map #(list % (my-goldbach %)) (range n (inc m))))))

(defn my-goldbach
  "Goldbach's conjecture."
  [n]
  (if (or (odd? n) (== n 2))
    nil
    (loop [ps (my-primes n)]
      (let [[p' & ps'] ps, m (first (drop-while #(> n (+ % p')) ps))]
        (if (and (not (nil? m)) (== (+ p' m) n))
          (list p' m)
          (recur ps'))))))

(defn my-primes
  [n]
  (loop [n n, [m & ms] (cons 2 (iterate #(+ 2 %) 3)), ps nil]
    (if (> m n)
      (reverse ps)
      (let [ps' (drop-while #(> (Math/pow % 2) m) ps),
            ps'' (if (every? #(not= (rem m %) 0) ps') (cons m ps) ps)]
        (recur n ms ps'')))))