I went and updated your code to incorporate my solutions, and in the process added a bunch of cases. Unfortunately this also caused your solution to generate warnings. I find it a touch suprising that my longer solution is the only one that works correctly on all the cases. Guys youve got to be more thorough in your testing!

use warnings;
use strict;
use Carp;
local $SIG{__WARN__}=sub {die("\t@{[(caller(1))[3]]}() generated warni
+ngs!\n")};

my $foo = {
     aa => { O => 'zz',  C => 'yy'  }, #
     bb => { O => 'xx',  C => 'xx'  },
     cc => { O => undef, C => 'ww'  }, #
     dd => { O => 'vv',  C => undef }, #
     ee => { O => undef, C => undef },
     ff => {             C => undef },
     gg => { O => 0,     C => 0     },
     hh => { O => undef, C => 0     }, #
     ii => { O => undef             }, #
     jj => { O => 0,     C => ' '   }, #
     kk => { O => ' ',   C => 0     }, #
     ll => { O => undef, C => ' '   }, #
     mm => { O => ' ',   C => undef }, #
};

sub BUK{local($^W,$a)=(0,pop);grep{!exists$a->{$_}{O}or$a->{$_}{O}ne$a
+->{$_}{C}}keys%$a}
sub snw{no warnings qw(uninitialized);my$h=pop;grep{$h->{$_}{O}ne$h->{
+$_}{C}}keys %$h}
sub sg_{my$h=pop;grep{!(defined($h->{$_}{O}&&$h->{$_}{C})&&$h->{$_}{O}
+eq$h->{$_}{C}||!defined($h->{$_}{O}||$h->{$_}{C}))}%$h}
sub eg_{my$h=pop;grep{!(($h->{$_}{O}||$;)eq($h->{$_}{C}||$;))}%$h}
sub ddf{$a=pop;grep{$b=$$a{$_};defined$$b{O}!=defined$$b{C}||defined$$
+b{O}&&$$b{O}ne$$b{C}}keys%$a}#98
sub dex{$a=pop;grep{$b=$$a{$_};exists$$b{O}!=exists$$b{C}||defined$$b{
+O}!=defined$$b{C}||defined$$b{O}&&$$b{O}ne$$b{C}}keys%$a}#126
sub tad{my($h)=@_;grep{!exists($h->{$_}->{O})||(defined($h->{$_}->{O})
+?(defined($h->{$_}->{C})?($h->{$_}->{O}ne$h->{$_}->{C}):1):defined($h
+->{$_}->{C}))}keys%$h}#162


print "      Required: aa cc dd ff hh ii jj kk ll mm\n";
print "---------------------------------------------\n";
eval { print "   tadman golf: @{[sort {$a cmp $b} tad($foo)]}\n"; };
print $@ if $@;

eval { print "BrowserUK golf: @{[sort {$a cmp $b} BUK($foo)]}\n"; };
print $@ if $@;

eval { print "sauoq No warns: @{[sort {$a cmp $b} snw($foo)]}\n"; };
print $@ if $@;

eval { print "    Sauoq golf: @{[sort {$a cmp $b} sg_($foo)]}\n"; };
print $@ if $@;

eval { print "  Elusion golf: @{[sort {$a cmp $b} eg_($foo)]}\n"; };
print $@ if $@;

eval { print " Demerphq defd: @{[sort {$a cmp $b} ddf($foo)]}\n"; };
print $@ if $@;

eval { print "Demerphq exist: @{[sort {$a cmp $b} dex($foo)]}\n"; };
print $@ if $@;
__END__
      Required: aa cc dd ff hh ii jj kk ll mm
---------------------------------------------
   tadman golf: aa cc dd ff hh jj kk ll mm
    main::BUK() generated warnings!
sauoq No warns: aa cc dd hh jj kk ll mm
    Sauoq golf: aa cc dd hh jj kk ll mm
  Elusion golf: aa cc dd jj kk ll mm
 Demerphq defd: aa cc dd hh jj kk ll mm
Demerphq exist: aa cc dd ff hh ii jj kk ll mm
[download]

Hmm, maybe it isnt so suprising considering its the longest with the exception of only tadmans solution

;-)

---
demerphq
my friends call me, usually because I'm late....

---

---

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