99 PSiE [Problem 8]

はじめに

Ninety-nine Problems, Solved in Elm を毎日ふれることで､Elm に親しもうという『日記』です｡詳細は 99 PSiE [Problem 1] をご覧ください｡

問題

Write a function to remove consecutive duplicates of list elements.
(引用元：Problem 8)

成果物

-- Ninety-nine Problems, Problem 8
-- https://johncrane.gitbooks.io/ninety-nine-elm-problems/content/p/p08.html
import Html

-- main = Html.text
--        <| Debug.toString
--        <| noDupes [1, 1, 2, 2, 3, 3, 3, 4, 5, 4, 4, 4, 4]

-- noDupes list =
--     case list of
--         x::xs ->
--             case xs of
--                 y::ys -> if x == y then
--                              [x] ++ noDupes ys
--                          else
--                              [x] ++ [y] ++ noDupes ys
--                 [] -> []
--         [] -> []

-- noDupes list = List.foldl (\x xs -> case xs of
--                                         y::ys -> ) [] list
noDupes list =
    let
        noDupCons y ys =
            case List.head ys of
                Nothing -> [y]
                Just a ->
                    if y == a then
                        ys
                    else
                        y::ys
    in
        List.foldr noDupCons [] list

-- Checker
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 " ++ (Debug.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" ]
            ]

正答例

=> Problem 8 Solutions

コメント

• "consecutive" って連続って意味なのか...
• 解けなかった｡くそったれ｡
• あぁ､Maybe つかうのか｡
• しかし Elm はなぜ Haskell で標準で利用できる関数群を消去していったのか｡謎は深まるばかりだ｡