Permutations of size \(k\). Modify Permutations from the previous exercise so that it takes two command-line arguments \(n\) and \(k\), and prints all \(P(n, k)=\) \(n ! /(n-k)\) ! permutations that contain exactly \(k\) of the \(n\) elements. Below is the desired output when \(k=2\) and \(n=4\) (again, do not worry about the order):

ab ac ad ba be bd ca cb cd da db dc