Oddly, the Haskell version of Quicksort is probably the easiest to understand:

qsort []     = []
qsort (x:xs) = qsort (filter (< x) xs) ++ [x] ++ qsort (filter (>= x) xs)

The second line reads: “to sort a list whose first element is x and the rest of which is called xs, sort the elements of xs that are less than x, sort the elements of xs that are greater than or equal to x, and concatenate (++) the results with x sandwiched in the middle.”

To learn more about quicksort’s behaviour see Eppstein’s paper. QuickSort source code download..