use strict;

my %p2C;
my %C2p;
key ('thequickbrownfoxjumpsoverthelazydogs',10);
printKeys(\%p2C);
printKeys(\%C2p);

sub printKeys {
    my $href = shift;
    print "\nCT: ";
    print(($_).' ') foreach (sort keys %{$href});
    print "\npt: ";
    print(($$href{$_}).' ') foreach (sort keys %{$href});
    print "\n";
}

sub key {
    my @kp = grep /[a-z]/, split //, shift;
    my $caesar= shift;
    my @alpha = ('A'..'Z');
    push @alpha, shift @alpha for (1..$caesar);
    foreach (@kp,'a'..'z') {
        if (not exists $p2C{$_}) {
            my $k = shift @alpha;
            $p2C{$_}=$k;
            $C2p{$k}=$_;
        }
    }
}

##</code><code>##

CT:   a b c d e f g h i j k l m n o p q r s t u v w x y z
pt:   F S Q I M X J L P Z R E A W U B N T C K O D V Y H G

CT:   A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
pt:   m p s v l a z y d g t h e q u i c k b r o w n f x j