Maybe this is aggogant, but I can't help thinking that the question is asked too late in the process.

while(<DATA>)
{
  # regex detects or doesn't detect number as $found in line
  m/magic_phrase:(\d+)/;
  next unless ( $found = $1 );
  $max = ( $found >$max ? $found : $max );
  $seen{$found}++;
}

sub isit
{
   return exists $seen{$_[0]};
}

# if you really need the output (or array)
for ( 1..$max)
{
    my $str = ( isit($_) ? "$_.found" : "$_.lost" );
    print "$str\n";
    push @array, $str;
} 

print "\@array is @array\n";
__DATA__
magic_phrase:2
magic_phrase:5
[download]

Produces:

1.lost
2.found
3.lost
4.lost
5.found
@array is 1.lost 2.found 3.lost 4.lost 5.found
[download]

--Bob Niederman, http://bob-n.com