Problem 8

Write a function to remove consecutive duplicates of list elements.

Example

noDupes [1, 1, 2, 2, 3, 3, 3, 4, 5, 4, 4, 4, 4]
    == [1, 2, 3, 4, 5, 4]

Unit Test

import Html
import List
import Maybe


noDupes : List a -> List a
noDupes xs =
    -- 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)
            [ noDupes [ 1, 1, 1, 1, 2, 5, 5, 2, 1 ] == [ 1, 2, 5, 2, 1 ]
            , noDupes [ 2, 1, 1, 1 ] == [ 2, 1 ]
            , noDupes [ 2, 2, 2, 1, 1, 1 ] == [ 2, 1 ]
            , noDupes [ 1 ] == [ 1 ]
            , noDupes [] == []
            , noDupes [ "aa", "aa", "aa" ] == [ "aa" ]
            , noDupes [ "aab", "b", "b", "aa" ] == [ "aab", "b", "aa" ]
            ]

Hints

1. How would you copy a list using foldr? How would you modify the function passed to foldr only copy new values?
2. How would you drop the head of the list if it's a duplicate? Can you apply that recursively to solve the problem?

Solutions

Solutions