f#

let obwod a b=a+2*b
obwod 1 2
let pole_trojkata (a:float) (b:float)= 0.5*a*b
pole_trojkata 1.0 2.0


//zad2

let x=3
let rec suma_mnozenia a =
    if a < 1 then 0
    else x + suma_mnozenia (a - 1)
suma_mnozenia 4

//zad 3
let x=2
let rec mnozenie_mnozenia a =
    if a < 1 then 1
    else x * mnozenie_mnozenia (a - 1)
mnozenie_mnozenia 3

//zad4
let rec e_s_l list buff bb =
  match list with
  | x::r -> if bb=true then (e_s_l r (x::buff) false) else (e_s_l r buff true)
  | [] -> List.rev buff
printf "exc.4 %A" (e_s_l [1;2;3;4;5;6;7;8;9] [] true)
//zad5

let rec_hr list =
  let bb = true
  list |> List.indexed|> List.filter(fun  (i, x)  -> i%2=0 ) |> List.map (fun (i, x) -> (x))
printf "exc.5 %A" (rec_hr [1;2;3;4;5;6;7;8;9] )


//zad6
let rec filter_by_n list buff n =
  match list with
  | x::r -> if x%n=0 then (filter_by_n r (x::buff) n) else (filter_by_n r buff n)
  | [] -> List.rev buff
printf "exc.6 %A" (filter_by_n [1;2;3;4;5;6;7;8;9] [] 3)

//zad7

let rec_hr list n = List.filter(fun x -> x%n=0 ) list
printf "exc.7 %A" (rec_hr [1;2;3;4;5;6;7;8;9] 3)

//zad 8
type Ksiazka={
    Tytul : string
    Autor : string
    Rok_wydania : int
    Wydawnictwo : string
    liczba_stron : int
    Twarda_oprawa : bool
    Miekka_oprawa : bool
    }

    //9-
let min_max_rec list =
  let rec min list got =
     match list with
    | x::rest -> if x<got then min rest x else min rest got
    | [] -> got
  let rec max list got =
    match list with
    | x::rest -> if x>got then max rest x else max rest got
    | [] -> got
  (min list list.[0], max list list.[0])
printfn "ex.9 %A" (min_max_rec [3;2;1;5;8;2])
//zad10
let min_max list = (List.min list, List.max list)
printfn "ex.10 %A" (min_max [3;2;1;5;8;2])

//11-
let average_rec list =
  let rec sum list got=
    match list with
    |x::rest -> sum rest (x + got)
    |[] -> got

  (sum list 0) / (List.length list)

printfn "ex 11 %A" (average_rec [1;2;3;4])

//12-
let average_high list =
  let sum list = List.fold (+) 0 list
  (float (sum list))/(float (List.length list))
printfn "ex 12 %A" (average_high [1;2;3;4])

//13-
let rec count_less list n count =
  match list with
  | x::rest ->if x<n then count_less rest n (count+1) else count_less rest n count
  |[] -> count
printfn "exc.13 : %A" (count_less [2;3;7;11;4;9] 5 0)

//14-
let less_n list n = list |> List.filter(fun x-> x>=n) |> List.length
printfn "ex.14 : %A" (less_n [2;3;7;11;4;9] 5)