「ClojureでNinety-Nine Lisp Problems(P11～15)」ブログ用

p11.clj

(defn my-encode
  "Run-length encoding of a list."
  [xs]
  (map #(list (count %) (first %)) (partition-by identity xs))
)

(defn my-encode-modified
  "Modified run-length encoding."
  [xs]
  (map #(let [[cnt elem] %] (if (== cnt 1) elem (list cnt elem))) (my-encode xs))
)

p12-1.clj

(defn my-decode
  "Decode a run-length encoded list."
  [xs]
  (flatten (map #(if (list? %) (replicate (first %) (second %)) %) xs))
)

p12-2.clj

(defn my-decode
  "Decode a run-length encoded list."
  [xs]
  (reduce #(concat %1 (if (list? %2) (replicate (first %2) (second %2)) (list %2))) nil xs)
)

p13-1.clj

(defn my-encode-direct
  "Run-length encoding of a list (direct solution)."
  [xs]
  (reverse (loop [[x & _ :as xs] xs, ys nil]
    (if (nil? x)
      ys
      (let [[[e & _ :as z] zs] (split-with #(= x %) xs),
            cnt (count z),
            elem (if (== cnt 1) e (list cnt e))]
        (recur zs (cons elem ys))
      )
    )
  ))
)

p13-2.clj

(defn my-encode-direct
  "Run-length encoding of a list (direct solution)."
  [xs]
  (map
    #(let [cnt (count %), elem (first %)]
      (if (== cnt 1) elem (list cnt elem))
    )
    (partition-by identity xs)
  )
)

p14.clj

(defn my-dupli
  "Duplicate the elements of a list."
  [xs]
  (reduce #(concat %1 (replicate 2 %2)) nil xs)
)

p15.clj

(defn my-repli
  "Replicate the elements of a list a given number of times."
  [xs n]
  (reduce #(concat %1 (replicate n %2)) nil xs)
)