http://qs1969.pair.com?node_id=87538

Converts a list of numbers to a string of ranges: (1,2,3,5,8,9,10,11) to "1-3,5,8-11".
use 5.6.0;  # for (??{ ... })

sub num2range {
  local $_ = join ',' => sort { $a <=> $b } @_;
  s/(?<!\d)(\d+)(?:,((??{$++1})))+(?!\d)/$1-$+/g;
  return $_;
}

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