(ns task_1)

;; p - prefix to add
;; a - list of elements
;; n - onumber of elements (count a)
;; ex - exclude
(defn permute_add [p, a, n]
  (if (= n 0)
    nil
    (if (= (nth a (- n 1)) (last p))
      (permute_add p a (- n 1))
      (concat
       (conj (permute_add p a (- n 1))
             (concat p (list (nth a (- n 1)))))))))

;; apply permute_add to every item of list
(defn permute_add_list [list, a, n, counter]
  (if (= counter (count list))
    (if (nil? list)
      (permute_add `() a n)
      nil)
    (concat
     (permute_add (nth list counter) a n)
     (permute_add_list list a n (+ counter 1)))))

(defn perm_of_len [a, n]
  (if (= n 0)
    nil
    (permute_add_list (perm_of_len a (- n 1)) a (count a) 0)))

(perm_of_len `(0 1 2 3) 2)