Permutations of size k$.$ Write a program that takes wo

arguments

n and

k$,$ and prints out all

P$($n$,$k$)=$ n$!($n$$k$)!$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 bc bd ca cb cd da db dc