Write a routine comb that when given a set of values and a non-negative integer
returns a list of all combinations of the values of size
.
For example
> comb( {a,b,c,d}, 3 );
{ {a,b,c}, {a,b,d}, {a,c,d}, {b,c,d} }
Modify your routine to work for lists which may contain duplicates, e.g.
> comb( [a,b,b,c], 2 );
[[a,b], [a,c], [b,b], [b,c]]