F#RunLengthEncoding.fsx

open System.Linq

// aabbbcdddd -> [(a,2), (b,3), (c,1), (d,4)]
let runLength (s: string) =
    let heads = { 1 .. s.Length - 1 }.Where(fun i -> s.[i - 1] <> s.[i]).Prepend(0).Append(s.Length).ToArray()
    { 0 .. heads.Length - 2 }.Select(fun i -> s.[heads.[i]], heads.[i + 1] - heads.[i]).ToArray()

// 使用例
input()
|> runLength
|> printfn "%A"

F# Run-Length Encoding
with LINQ

string -> (char*int)[]