and another approach:

my @keys = reverse sort {$hash{$a} <=> $hash{$b} || $a cmp $b} (keys %
+hash);
my @idx = ( ( map { $_, $_+1+$#keys/2 } 0..$#keys/2-1 ), $#keys%2?():$
+#keys/2 );
for(my $i=shift(@idx); defined $i; $i=shift(@idx) ){
  print $keys[$i];
  ($i = shift(@idx)) && print "\t" . $keys[$i];
  print "\n";
}
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