「ClojureでNinety-Nine Lisp Problems(P21～25)」ブログ用

p21-1.clj

(defn my-insert-at
  "Insert an element at a given position into a list."
  [x xs n]
  (reverse (first (reduce (fn [[elems cnt] elem]
    [(if (not= cnt n) (cons elem elems) (cons elem (cons x elems))), (inc cnt)]
  ) [nil, 1] xs)))
)

p21-2.clj

(defn my-insert-at
  "Insert an element at a given position into a list."
  [x xs n]
  (let [[f s] (split-at (dec n) xs)] (concat f (cons x s)))
)

p22.clj

(defn my-range
  "Create a list containing all integers within a given range."
  [n m]
  (reverse (
    #(if (> %1 %2)
      %3
      (recur (inc %1) %2 (cons %1 %3)))
    n m nil)
  )
)

p23-1.clj

(defn my-remove-at
  "Remove the K'th element from a list."
  [xs n]
  (let [[f s] (split-at (dec n) xs)] (concat f (rest s)))
)

(defn my-rnd-select
  "Extract a given number of randomly selected elements from a list."
  [xs n]
  (#(if (>= (count %2) n)
      %2
      (let [n (rand-int (count %1))]
        (recur (my-remove-at %1 n) (cons (nth %1 n) %2))
      )
    ) xs nil)
)

p23-2.clj

(defn my-rnd-select
  "Extract a given number of randomly selected elements from a list."
  [xs n]
  (defn my-remove-at
    [xs n]
    (let [[f s] (split-at n xs), [elem & rst] s] [elem (concat f rst)])
  )
  (#(if (>= (count %2) n)
      %2
      (let [n (rand-int (count %1)), [elem lst] (my-remove-at %1 n)]
        (recur lst (cons elem %2))
      )
    ) xs nil)
)

p23-3.clj

(defn my-rnd-select
  "Extract a given number of randomly selected elements from a list."
  [xs n]
  (#(if (>= (count %2) n)
      %2
      (let [[fst & rst] (shuffle %1)]
        (recur rst (cons fst %2))
      )
    ) xs nil)
)

p24-1.clj

(defn my-rnd-select
  "Extract a given number of randomly selected elements from a list."
  [xs n]
  (#(if (>= (count %2) n)
      %2
      (let [[fst & rst] (shuffle %1)]
        (recur rst (cons fst %2))
      )
    ) xs nil)
)

(defn my-lotto-select
  "Lotto: Draw N different random numbers from the set 1..M."
  [n m]
  (my-rnd-select (range 1 (inc m)) n)
)

p24-2.clj

(defn my-lotto-select
  "Lotto: Draw N different random numbers from the set 1..M."
  [n m]
  (let [n (min n m)]
    (list*
      (#(if (>= (count %) n)
          %
          (recur (conj % (inc (rand-int m))))
        ) #{}
      )
    )
  )
)

p25.clj

(defn my-rnd-permu
  "Generate a random permutation of the elements of a list."
  [xs]
  (reduce
    #(if (== 0 (rand-int 2))
        (cons %2 %1)
        (concat %1 (list %2))
      ) nil xs)
)