use strict;
use warnings;

my $string = "aaaggctt";
my %hash = qw(a t g c c g t a);

print "The DNA string is: \n";
print $string,"\n";
print "The reverse complement is: \n";

#One way to do it... 1st chunk..
for (my $i = length($string); $i>= 0 ; $i--){
        for (keys %hash){
                print substr($string, $i, 1) eq $_ ? $hash{$_} : '';
                }
        }


print "\n"

#Expansion of the previous solution.. 2nd chunk..
for (my $i = length($string); $i>= 0 ; $i--){
        for (keys %hash){
                if(substr($string, $i, 1) eq $_ ){
                        print $hash{$_};
                        }
                }
        }