#!/usr/bin/perl
use strict;
use warnings;
use Algorithm::Loops 'NestedLoops';
use Text::Levenshtein 'fastdistance';

my $seed = $ARGV[0] || '000';
my $iter = NestedLoops([([0..3]) x length($seed)]);

while (my @list = $iter->()) {
    my $neighbor = join '', @list;
    print "$neighbor\n" if fastdistance($neighbor, $seed) < 3;
}