Or using a data pipeline with sort and grep:

use strict;
use warnings;

my @strings = qw( 12-12 12-12-12 12-13-12-13 12-12-13-13 12-13-13-14 )
+;
 
for (@strings) {
    my $prev = -1; # numbers being separated by dashes, I assume that 
+a negative value is not possible
    print join "-", grep {$prev != $_ and $prev = $_} sort {$a <=> $b}
+ split /-/, $_;
    print "\n";
}
[download]

which prints:

12
12
12-13
12-13
12-13-14
[download]