99 Clojure Problems – 12: Decode a Run-length Encoded List

Given a run-length code list generated as specified in problem P10, construct its uncompressed version.

Example:

(deftest p12-decode
  (is (= '( a a a a b c c a a d e e e e) (decode '((4 a) (1 b) (2 c) (2 a) (1 d) (4 e))) )))

Solution:

Again, the solution to this problem is fairly straightforward: We map the encoded list over a function that applies Clojure's built-in repeat to each sublist's second element (the character) as many times as the first element of the sublist specifies. This leaves us with a list of lists, each containing the repeating elements. We obtain the final result by flattening the nested structure in to a single list.

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