ovid-puzzle

#!perl

=head http://blogs.perl.org/users/ovid/2014/12/a-small-puzzle-for-you.html

Given several arrays, each of which has elements which are a subset of allowed elements,
and given that every allowed element appears at least once in each array,
how do I rewrite all arrays such that each element of each array which has an identical value to an element
in another array has the same index number in each array, with missing elements being undef?

=cut

@a = ( 'b', 'c', 'f' );
@b = ( 'a', 'd' );
@c = ( 'c', 'd', 'e' );

my @arrs = (\@a, \@b, \@c);
my %h;
$h{$_}++ for map{ +(@$_) } @arrs;
my @list = sort keys %h;

my @new_arrs;
for( my $i = 0; $i < @list; $i++ ){
    for(my $a = 0; $a < @arrs; $a++){
        my $val = $list[$i];
        $val = undef unless( grep {$list[$i] eq $_ } @{$arrs[$a]} );
        push @{$new_arrs[$a]}, $val;
    }
}

use Data::Dumper;
$Data::Dumper::Indent = 1;
print Dumper \@new_arrs;