Question

I need to switch 2 elements on entered indexes in list in Scheme lang. For example:

(swap-index 0 3 ‘(1 2 3 4 5))

(4 2 3 1 5)

Can someone help? Thanks in advance! 🙂

Answer 1

Here is solution in clojure. I hope algorithm would be helpful.

(defn split [idx lst]
  (let [lst-rest (drop idx lst)]
   [(take idx lst) (first lst-rest) (rest lst-rest)]))

(defn swap-index [idx1 idx2 lst]
  (let [[lst1 e1 lst] (split idx1 lst)
        [lst2 e2 lst3] (split (dec (- idx2 idx1)) lst)]
    (concat lst1 [e2] lst2 [e1] lst3)))

=> (swap-index 0 3 [1 2 3 4 5])
   (4 2 3 1 5)