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; P12 Decode a run-length encoded list.
; Given a run-length code list generated as specified in problem P11.
; Construct its uncompressed version.
(def a (list (list 4 "a") "b" (list 2 "c") (list 2 "a") "d" (list 4 "e")))
(func extend (lst1 lst2)
(reduce append lst2 lst1))
(func flatten (lst)
(reduce
(lambda (x y) (extend x y))
lst
(list)))
(func decode (lst)
(flatten
(map
(lambda (item)
(if (eq? 1 (length item))
(list item)
(rpt (first item) (last item))))
lst)))
(func rpt (cnt let)
(if (eq? cnt 1)
(list let)
(extend (list let) (rpt (- cnt 1) let))))
; iterative
(func rpt-iter (cnt let)
(def out (list))
(for-count cnt
(redef out (append out let)))
out)
(print (->string (decode a)))
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