#! /usr/bin/perl -w

use strict;

# build our encoder and decoder
my $offset = 0;
my %encode;
my %decode;
for my $x( qw/A C G T/ ) {
  for my $y( qw/A C G T/ ) {
    for my $z( qw/A C G T/ ) {
       $encode{"$x$y$z"} = $offset;
       $decode{$offset}  = "$x$y$z";
       $offset++;
    }
  }
}

# encode the string
my $in = shift || 'AAAACTGACCGTTTT';
my $enc = '';
while( $in =~ /(...)/g ) {
  $enc .= chr( 48 + $encode{$1} );
}
print "encoded: $enc\n";

# and back again
my $dec = '';
for( split //, $enc ) {
  $dec .= $decode{ ord($_) - 48 };
}

print "decoded: $dec\n";