Assuming the test harness provided, I doubt anyone can beat this:

sub f{d,c,b,a,f,e}
[download]

Try this for a test harness:

my @list = (
     a => [ 'b', 'c', 'e' ],
     b => [ 'd' ],
     c => [ 'b', 'd' ],
     f => [ 'a' ],
);
print join (',', map { "'$_'" } f(@list)),"\n";
[download]

Your code produces 'd','b','c','f','e','a', which does not reflect the fact that 'f' depends on 'a'.

So, I am afraid your solution holds only for a limited set of test harnesses -- and is certainly not the shortest among such solutions.

The Sidhekin
print "Just another Perl ${\(trickster and hacker)},"