#!/usr/bin/perl

# SPDX-FileCopyrightText: Chris Pressey, the original author of this work, has dedicated it to the public domain.
# For more information, please refer to <https://unlicense.org/>
# SPDX-License-Identifier: Unlicense

my %rule = (
	'12' => '11',
	'122' => '12',
	'112' => '21',
	'1122' => '22'
);

my $k = $ARGV[0] or "122112122122112112212112122";
$s = $k;

foreach my $key (sort { length($b) <=> length($a) } keys %rule) {
	print "$key -> $rule{$key}\n";
}
print "\n";

printf "%5d: $s\n", 0;
$done = 0;
$n = 1;
while (not $done) {
	$done = 1;
	foreach my $key (sort  { length($b) <=> length($a) } keys %rule) {
		my $klen = length($key);
		if (substr($s, (length($s) - $klen)) eq $key) {
			$s = $rule{$key} . substr($s, 0, length($s)-$klen);
			$done = 0;
			last;
		}
	}
	printf "%5d: ${spc}$s\n", $n;
	if ((index $s, "111") != -1 or index($s, "222") != -1) {
		print "illegal string\n";
		last;
	}
	$n++;
}