my %hits;
while( <> ) {
  my( $key ) = /HIT:\s+(\S+)/;
  $hits{ $key }++;
}
my @distinct = keys %hits;

##</code><code>##

my @hits;
my %seen;
while( <> ) {
  my( $key ) = /HIT:\s+(\S+)/;
  next if $seen{ $key }++;
  push @hits, $key;
}