The inner loop can be replaced with a hash to change the algorithm from O(N2) to O(N), a major improvement. 

my @groups;
my %in_num_groups;
while (@pile) {
    my $item = shift @pile;
    push @{$groups[$in_num_groups{$item}++]}, $item;
}

[download]

I also fixed the needless use of a reference to the array of groups and the inability to store false values in @pile.

Update: For fun, did you know @pile could also be initialized using 

@pile = shuffle( (@card) x $n );

[download]

In reply to Re: 52 Perl Pickup by ikegami
in thread 52 Perl Pickup by dogz007

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