@array = ('x', 'x', 'y', 'z', 'z', 'z');
my %items;
for my $i (0 .. $#array) {
    $items{$array[$i]} ||= [ $i, $i ];  # only assigns for the first occurrence
    $items{$array[$i]}[1] = $i;         # replaces for every new occurrence
}

use Data::Dumper;
print Dumper \%items;

##</code><code>##

$VAR1 = {
          'x' => [
                   0,
                   1
                 ],
          'y' => [
                   2,
                   2
                 ],
          'z' => [
                   3,
                   5
                 ]
        };