use strict;
use warnings;

my @list = sort {$a <=> $b} (1, 2, 3, 6, 9, 10, 13, 22, 20, 19, 15, 21);
printf "%s\n", join(",", @list);

my @newList;
my ($min, $max);
for(@list, undef) {
  if(! defined($min)) { $min = $max = $_; }
  elsif(defined($_) && $_ == ($max + 1)) { $max++ }
  else {
    if($min == $max) { push @newList, ($min, $_) }
    else { push @newList, ("$min-$max", $_) }
    $min = $max = undef;
  }
}
pop @newList;

printf "%s\n", join(",", @newList);