99 PSiE [Problem 12]

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

Decompress the run-length encoded list generated in Problem 11.
(引用元：Problem 12)

成果物

import Html

type  RleCode a = Run Int a | Single a

-- my solution
rleDecode_ listOfRleCode = List.map fromRleCode listOfRleCode |> List.concat

fromRleCode rleCode =
    case rleCode of
        Run num b -> List.repeat num b
        Single b -> [b]

-- main = Html.text
--        <| Debug.toString
--        <| rleDecode
--        <| [Run 4 1, Single 2, Run 2 5, Single 2, Single 1]

-- Their solution
rleDecode listOfRleCode = List.concatMap fromRleCode listOfRleCode

-- answer check
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)
            [ rleDecode [ Run 4 1, Single 2, Run 2 5, Single 2, Single 1 ]
                == [ 1, 1, 1, 1, 2, 5, 5, 2, 1 ]
            , rleDecode [ Run 4 1, Single 2, Run 2 5, Single 2, Single 1 ]
                == [ 1, 1, 1, 1, 2, 5, 5, 2, 1 ]
            , rleDecode [ Run 4 "1", Single "b", Run 2 "5", Single "2", Single "a" ]
                == [ "1", "1", "1", "1", "b", "5", "5", "2", "a" ]
            ]

正答例

=> Problem 12 Solutions

コメント

へぇ～､List.concatMap ってこんな感じで使うのかー｡