my $string = "alpha beta beta gamma gamma   gamma foo bar bar baz qux qux qux";

# preseving the order
my $i;
my %h = map { $_ => $i++ } split(/[\b\s]+/,$string);
print join(" ", sort { $h{$a} <=> $h{$b} } keys %h);
print "\n";

# destroying the order
my %h = map { $_ => 1 } split(/[\b\s]+/,$string);
print join(" ",keys %h);
print "\n";

##</code><code>##

alpha beta gamma foo bar baz qux
foo gamma baz bar beta alpha qux