#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1168288

use strict;
use warnings;

my @ra = qw(0001 0002 0003 011 012 013 015 16 17 18 20);

$_ = join ',', @ra;

s/\b(\d+)(?{$1})\K(?:,(\d+)\b(??{++$^R!=$2||length$1!=length$2}))+/-$2/g;

print;