99 Clojure Problems – 15: Duplicate the Elements of a List a Given Number of Times

Example:

(deftest p15-duplicate-n
  (is (= '(a a a b b b c c c c c c d d d) (duplicate-n 3 '(a b c c d)))))

Solution:

Again, the solution is just a slight variation on the solution to the previous problem. We are reducing the list into an accumulator as before, but this time we use Clojure's built-in 'repeat' to achieve the specified number of duplications per element. 'Repeat' is returning a list so we have to concat the accumulator with the repeated elements to get our results back.

This is a two star problem, meaning it should take an experienced programmer about 60-90 minutes to solve. Presumably this problem is much harder to solve in Prolog than in Clojure.

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