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

##</code><code>##

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

##</code><code>##

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