Algo to find Permutation of say [a,b,c,d]

[jackdaniels]

I want to find the permutations of say 4 letters - a, b, c, d taken from 1 at a time to the number of elements (4 in this case).  Need to print out the possible values - What is the best algoritm to achieve this?

e.g. result should have:
a
ab
ba
abc
abd
bda
bdc
bdca
abcd
b
bc
...
etc
(all possibilities that can be made with the elements)

[Denis]

You have to generate combinations C(4, 1), ... C(4, 4) with only difference, that now order matters [a, b] != [b, a]. If you algorithm's code in Java/C++, let me know.