Quicksort (Haskell)

module Quick_sort where

partition p [] = ([],[])

partition p (x:rest) = if p x then (x:l,r) else (l,x:r)

where (l,r) = partition p rest

{-

sau

partition p (x:rest)

| p x = (x:l,r)

| otherwise = (l,x:r)

where (l,r)= partition p rest

-}

-- Varianta 1

qsort [] = []

qsort (x:ls) = qsort l ++ [x] ++ qsort r

where (l,r) = partition (<= x) ls

-- Varianta 2

qs [] = []

qs (x:ls) = qs l ++ [x] ++ qs r

where l = [y | y <- ls, y <= x]

r = [y | y <- ls, y > x]

-- Varianta 3

qss [] = []

qss (x:ls) = let l = [y | y <- ls, y <= x]

r = [y | y <- ls, y > x]

in qss l ++ [x] ++ qss r