@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;