Shohei Yoshida
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Shohei Yoshida's Blog

LeetCode 17. Letter Combinations of a Phone Number in F#

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Shohei Yoshida
·May 9, 2022·

1 min read

URL

leetcode.com/problems/letter-combinations-o..

Code

github.com/syohex/dotnet-study/blob/master/..

let letterCombinations (digits: string) : string list =
    let table =
        [| [ 'a'; 'b'; 'c' ]
           [ 'd'; 'e'; 'f' ]
           [ 'g'; 'h'; 'i' ]
           [ 'j'; 'k'; 'l' ]
           [ 'm'; 'n'; 'o' ]
           [ 'p'; 'q'; 's'; 'r' ]
           [ 't'; 'u'; 'v' ]
           [ 'w'; 'x'; 'y'; 'z' ] |]

    let rec letterCombinations' indexes (acc: char list) =
        match indexes with
        | [] ->
            let s = acc |> List.rev |> System.String.Concat
            [ s ]
        | h :: t ->
            table.[h]
            |> List.fold
                (fun v c ->
                    let ret = letterCombinations' t (c :: acc)
                    ret @ v)
                []


    if System.String.IsNullOrEmpty digits then
        []
    else
        let indexes =
            digits
            |> Seq.map (fun c -> int c - int '0' - 2)
            |> Seq.toList

        letterCombinations' indexes [] |> List.rev
 
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