#!/usr/bin/perl -w
use strict;
use Data::Dumper;
use Carp;

# If possible we prefer not to use any CPAN module
# or regex. It's for my understanding


my $seed = $ARGV[0] || "000"; 
# Seed can be longer than 3 digits but always 0,1,2,3

for (my $i = 0; $i < length($seed); $i++) {

    # First loop is to generate 1 position differ
    for (my $bs=1; $bs<=3; $bs++) {

        my $bval = $bs;
        if ( substr($seed,$i,1) == $bs) {
            $bval = 0;

        }

        my $ns = $seed;
        substr($ns,$i,1,$bval);
        print "$ns\n";


        # Second loop for tags in 2 positions differ

        for (my $j=($i+1); $j < length($seed); $j++) {

            for (my $cs = 1; $cs<=3;$cs++) {

                my $cval = $cs;
                if (substr($ns,$j,1) == $cs) {
                    $cval = $cs;
                }

                 my $ns2 = $ns;
                 substr($ns2,$j,1,$cval);
                 print "\t$ns2\n";

            }
        }


    }