maybe you'll consider hashes? 
while(<DATA>){
%h = ();
undef $h{$1} while(s/(\d\d)//);
print join ("-", sort keys %h),"\n";
}

__DATA__
12-12
12-12-12
12-13-12-13
12-12-13-13
12-13-13-14

[download]
updated
$h{$1} = null became undef $h{$1}
thank you Mr. choroba

In reply to Re: How can I reduce this with a REGEX? by Lennotoecom
in thread How can I reduce this with a REGEX? by misterperl

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