#!/usr/bin/perl
use strict;

my ($min,$max) = (0,21);
my @nums = (1, 5, 6, 8, 15, 20);
my $pad = 1;

my (%printed,%nums);
map { $nums{$_}++ } @nums;
for my $i (@nums) {
  for my $n ($i-$pad .. $i+$pad) {
    if ( ! $printed{$n} && $min <= $n && $n <= $max ) {
      print exists $nums{$n} ? "Highlighted: " : "";
      print $n, "\n";
      $printed{$n}++;
    }
  }
}