Write an F# function cut xs that cuts a list into two equal parts: Assume that t

Question

Write an F# function cut xs that cuts a list into two equal parts:

Assume that the list has even length.

To implement cut, first define an auxiliary function gencut(n, xs) that cuts xs into two pieces, where n gives the size of the first piece:

Paradoxically, although gencut is more general than cut, it is easier to write! (This is an example of Polya's Inventor's Paradox: "The more ambitious plan may have more chances of success.")

Another Hint: To write gencut efficiently, it is quite convenient to use F#'s local let expression

Explanation / Answer

let cut xs = gencutdata((List.length xs) / 2, xs)

let rec gencutdata(n, listdata) =
let rec cut n (listvalue : int list) (listdata : int list) =
match (n , listdata ) with
| 0, _ -> listvalue, listdata
| _, [] -> listvalue, listdata
| _, b :: listdata -> cut (n - 1) (List.rev (b :: listvalue )) listdata
cut n [] listdata

In the above program gencutdata function will be called recursivly and that cuts xs into two pieces.

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