$re = '/^(?=\d{1,2}([wp])(?:\d{1,2}(?!\1)[wp]\d{1,2}\1)*(?:\d{1,2}(?!\1)[wp])?$)\d{1,2}[wp]|(?!^)\G\d{1,2}[wp]/m';
$str = '2w
1p
3w1p3w
2p12w2p3w
2p12p2w3p
2p121w2p3w
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php