How to get all categories that have childrens?

what is the best way?

do i have to do custom loop, or can achieve this by doing multiple loops around the object, but this gonna effect the performance.

now i have this:

$scats = get_categoires();
foreach($scats as $scat) {
	if (!$scat->category_parent) {
		// do stuff
	}
}

but i need to filter duplicates categories assigned to the same parent.