Win8 Strawberry 5.30.3.1 (64)  Sat 09/26/2020 12:14:28
C:\@Work\Perl\monks
>perl
use strict;
use warnings;

my $n_found;
my $string = 'AKQJT98765432KKKK';
my $set = 'AQK';

# s/// probably fastest in practice.
my $destroy = $string;  # s/// alters its target
$n_found = $destroy =~ s{ [\Q$set\E] }{}xmsg;
print "s///:  Num of '$set' in '$string' == $n_found \n";

# m// probably a bit slower, use of =()= a bit tricky.
$n_found =()= $string =~ m{ [\Q$set\E] }xmsg;
print "m//:   Num of '$set' in '$string' == $n_found \n";

# tr/// is fastest, but needs expensive eval for arbitrary sets.
$n_found = $string =~ tr/KAQ//;
print "tr///: Num of 'KAQ' in '$string' == $n_found \n";

__END__
s///:  Num of 'AQK' in 'AKQJT98765432KKKK' == 7
m//:   Num of 'AQK' in 'AKQJT98765432KKKK' == 7
tr///: Num of 'KAQ' in 'AKQJT98765432KKKK' == 7