Problem 15

Repeat each element of a list a given number of times.

Example

repeatElements 3 [1, 2, 3, 3] == [1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 3, 3]

Unit Test

import Html 
import List


repeatElements : Int -> List a -> List a
repeatElements count list =
    -- your implementation goes here
    []


main : Html.Html a
main =
    Html.text
        <| case test of
            0 ->
                "Your implementation passed all tests."

            1 ->
                "Your implementation failed one test."

            x ->
                "Your implementation failed " ++ (toString x) ++ " tests."


test : Int
test =
    List.length
        <| List.filter ((==) False)
            [ repeatElements 2 [ 1, 2, 5, 5, 2, 1 ] == [ 1, 1, 2, 2, 5, 5, 5, 5, 2, 2, 1, 1 ]
            , repeatElements 4 [ 1, 2 ] == [ 1, 1, 1, 1, 2, 2, 2, 2 ]
            , repeatElements 4 [] == []
            , repeatElements 0 [ 1, 2 ] == []
            , repeatElements (-1) [ 1, 2 ] == []
            , repeatElements 40 [ 1 ] == [ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 ]
            , repeatElements 4 [ "1", "2" ] == [ "1", "1", "1", "1", "2", "2", "2", "2" ]
            ]

Hints

1. Do I need to repeat myself? "Recurse!"
2. Another solution uses List.concatMap
3. Fold!

   Solutions

   Solutions