This should meet your readability and efficiency criteria :

use strict;
use warnings;

my @chars = qw( a b c ? : ! f g ) ;
my %upchars ;

@upchars{@chars} =  ( 'A', 'B', 'C', undef, undef, undef, 'F', 'G' ); 
+# getUpperCaseChars( @chars );

my @charsWithNoUpperCase = grep {! defined $upchars{$_} } @chars;
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