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; P13 Run-length encoding of a list (direct solution).
; Implement the so-called run-length encoding data compression method directly.
; I.e. don't explicitly create the sublists containing the duplicates, as in problem P09,
; but only count them. As in problem P11, simplify the result list by replacing the
; singleton lists (1 X) by X.
(def a (list "a" "a" "a" "a" "b" "c" "c" "a" "a" "d" "e" "e" "e" "e"))
(func encode-direct (lst)
(encode-direct lst "" (list)))
(func encode-direct (lst :nil prev acc)
acc)
(func encode-direct (lst :{:any} prev acc)
(if (eq? (first lst) prev)
(encode-direct
(rest lst)
prev
(append (most acc)
(if (list? (last acc))
(list (+ 1 (first (last acc))) prev)
(list 2 prev))))
(encode-direct
(rest lst)
(first lst)
(append acc (first lst)))))
(print (->string a))
(print (->string (encode-direct a)))
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