你应该擅长:

preg_match_all("/\b([a-z]+[A-Z]+[a-zA-Z]*|[A-Z]+[a-z]+[a-zA-Z]*)\b/", $input, $matches);
print_r($matches[1]); 

因为不需要捕获，所以也可以>>

As capturing is not needed, it can be also >>

preg_match_all("/\b(?:[a-z]+[A-Z]+[a-zA-Z]*|[A-Z]+[a-z]+[a-zA-Z]*)\b/", $input, $matches);
print_r($matches[0]);