Алгоритм генерації стрічок 1 | 11 | 21 | 1211 | 111221 etc

gistfile1.php

<?php
class Generator {
	private $start = '1';
	
	function __construct($start = null) {
		if ($start != null) {
			$this->start = (string) $start;
		}
	}

	public function ff($string, $r) {
		$char = $string[0];
		$count = 0;
		$index = 0;
		for ($i = 0, $total = strlen($string); $i < $total; $i++) {
			if ($string[$i] != $char) {
				$index = $i;
				break;
			}
			$count ++;
		}

		if ($index == 0) {
			$index = $total;
		}

		return array(
			$count . $char,
			($index + $r)	
		);
	}

	public function run($n = 6) {
		$start = $this->start;
		while ($n > 0) {
			$this->log[] = $start;

			$end = '';
			$i = 0;
			$total = strlen($start);

			while ($i < $total) {
				list($string, $i) = $this->ff(substr($start, $i), $i);
				$end .= $string;
			}

			$start = $end;
			$n --;
		}
		return $this;
	}

	public function getLog() {
		foreach ($this->log as $number => $value) {
			echo ($number + 1), " - ", $value, "\n";
		}
	}
}

$g = new Generator(3);
$g->run()
	->getLog();