/**
* @param BinaryTree $node
*
* @return BinaryTree|null
*/
protected function balance(BinaryTree $node = null)
{
if ($node === null) {
return null;
}
$diff = $node->leftHeight() - $node->rightHeight();
if ($diff < -1) {
// right side is taller
$node = $this->rotateLeft($node);
} elseif ($diff > 1) {
// left side is taller
$node = $this->rotateRight($node);
}
return $node;
}
