validating

Make that:

for my $dimension ( \@row, \@col, \@block )
{
    for my $grouping ( @$dimension )
    {
        my @defined = grep { defined } map { $$_ } 
                      @$grouping;   

        my %seen;
        return if grep { $seen{$_}++ } @defined;
    }
}

Now we can test partially solved puzzles too.