Perl Christmas Quiz

[Hakim Cassimally]

On 12/12/2008, Peter Corlett <abuse at cabal.org.uk> wrote:
> On Fri, Dec 12, 2008 at 01:18:24PM +0000, Hakim Cassimally wrote:
>  [...]
>
> > The question isn't specific about how the output should look if it a key
>  > doesn't appear in both arrays, or if n==m.
>
>
> It does. It asks for the "intersect", which is the set theory way of saying
>  "those elements that appear in both sets, and no others".
>
>  Here's my attempt:
>
>  sub intersect{my%x;$x{$_}++for(@{+shift});grep{$x{$_}&&$x{$_}--}@{+shift};}

Gah of course: though you missed the min(n,m) requirement. So
sub uniqc { my %seen; $seen{$_}++ for @_; \%seen }
sub intersect {
    my @lists = map uniqc(@$_), @_;
    +{  map {
        my $key = $_;
        my @vals = grep $_, map { $_->{$key} } @lists;
        @vals == @lists ?
            do {
                my ($min, $max) = (sort {$a<=>$b} @vals)[0,-1];
                ($key => $min==$max ? $min : "min($min,$max)");
            }
        : ();
        } keys %{ uniqc map @$_, @_ }
    }
}