99 Clojure Problems – 10: Run-length Encoding of a List

Use the result of problem P09 to implement the so-called run-length encoding data compression method. Consecutive duplicates of elements are encoded as tuples (N, E) where N is the number of duplicates of the element E.

Example

(deftest p10-encode
  (is (= '((4 a) (1 b) (2 c) (2 a) (1 d) (4 e)) (encode '( a a a a b c c a a d e e e e) ))))

Solution:

My simple solution maps over the result of problem 9 using a mapping function that replaces each sublist with a tuple consisting of the length of the sublist and the element.

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