/// Use the result of problem P09 to implement the so-called run-length

/// encoding data compression method. Consecutive duplicates of elements

/// are encoded as lists (N E) where N is the number of duplicates of the element E.

///

/// Example:

/// * (encode '(a a a a b c c a a d e e e e))

/// ((4 A) (1 B) (2 C) (2 A) (1 D)(4 E))

///

/// Example in F#:

///

/// encode <| List.ofSeq "aaaabccaadeeee"

/// val it : (int * char) list =

/// [(4,'a');(1,'b');(2,'c');(2,'a');(1,'d');(4,'e')]

let combine item = function

| (innerHead::innerTail)::outerTail when innerHead=item -> (item::innerHead::innerTail)::outerTail

| nomatchy -> [item]::nomatchy

let pack list =

List.foldBack combine list []

let runlengthInner item state =

(List.length item, List.head item)::state

let runlength list =

List.foldBack runlengthInner list []

let runLength_after_solution_of_course_use_map l =

l |> List.map (fun x -> List.length x, List.head x)

List.ofSeq "aaaabccaadeeee" |> pack |> runLength_after_solution_of_course_use_map |> printfn "%A"