Simplify?

for ($#history .. 0) {
    my $temp = pop @history;
    next if exists $history{ $temp };
    $history{ $temp } ++;
    unshift @history;
}
[download]

Why not follow through when you get to that point? Something like this seems just fine to me:

my %seen;
for (1 .. @history) {
    my $item = pop @history;
    unshift @history, $item unless $seen{$item}++;
}
[download]

Sure, the temporary variable is still there. But then, do you really prefer something along these lines?

my %seen;
for (1 .. @history) {
    unshift @history, $seen{$history[-1]}++ ? $#history-- && () : pop 
+@history;
}
[download]

I didn't think so either. ;-)

— Arien