Correct Answer (Detailed Explanation is Below)
A.
Height of left subtree minus height of right subtree
Detailed Explanation
The
balance factor of an AVL tree node is commonly defined as
height(left subtree) - height(right subtree). For a valid AVL tree, the balance factor of every node must be
-1, 0, or +1. A factor of 0 means both subtrees have equal height, while +1 means the left subtree is one level taller and -1 means the right subtree is one level taller. Values outside this range require rebalancing.
