There is an array with an already existing set of elements, for example:
[A] [B] [C] [D] [E] [F]
that is, n-elements.
It is necessary to place them in a smaller array of k-elements in size without repetitions, to get all possible options in this case by the formula without taking into account the order and without return should get 40 options. How to implement such an algorithm, preferably on java.
