use warnings;
use strict;

my @data = qw/0 6:4 12:8 19:31/;
my %nums = map { ( $_ => undef ) } 0 .. 31;
map {
    local @_ = sort { $a <=> $b } split /:/;
    for (my $n = $_[0]; $n < ( @_ == 1 ? $_[0] + 1 : $_[1] + 1 ); $n++ ) {
        delete $nums{$n};
    }
} @data;
print "$_\n" foreach sort keys %nums;