$re = '/\b(house|car)(?: (?!(?:house|car)\b)\w+){1,10} (?!\1)(house|car)\b/m';
$str = 'car word1 word2 word3 word4 word5 word6 word7 word8 word9 word10 house
house word1 word2 word3 word4 word5 word6 word7 word8 word9 word10 car
house word1 word2 word3 word4 word5 word6 word7 word8 word9 word10 word 11 car
car test car
house test house
house house house
car car car
this is a test house riding a new car
testing a car when testing a house test test test test test test test test test test test test house';
preg_match_all($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