如果链接断开，这里是代码。
class Combinations implements Iterator{ protected $c = null; protected $s = null; protected $n = 0; protected $k = 0; protected $pos = 0; function __construct($s, $k) { if(is_array($s)) { $this->s = array_values($s); $this->n = count($this->s); } else { $this->s = (string) $s; $this->n = strlen($this->s); } $this->k = $k; $this->rewind(); } function key() { return $this->pos; } function current() { $r = array(); for($i = 0; $i < $this->k; $i++) $r[] = $this->s[$this->c[$i]]; return is_array($this->s) ? $r : implode('', $r); } function next() { if($this->_next()) $this->pos++; else $this->pos = -1; } function rewind() { $this->c = range(0, $this->k); $this->pos = 0; } function valid() { return $this->pos >= 0; } protected function _next() { $i = $this->k - 1; while ($i >= 0 && $this->c[$i] == $this->n - $this->k + $i) $i--; if($i < 0) return false; $this->c[$i]++; while($i++ < $this->k - 1) $this->c[$i] = $this->c[$i - 1] + 1; return true; }}foreach(new Combinations("1234567", 5) as $substring) echo $substring, ' ';12345 12346 12347 12356 12357 12367 12456 12457 12467 12567 13456 13457 13467
13567 14567 23456 23457 23467 23567 24567 34567
