Given the `head`

of a singly linked list where elements are **sorted in ascending order**, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of *every* node never differ by more than 1.

**Example 1:**

**Input:** head = [-10,-3,0,5,9]

**Output:** [0,-3,9,-10,null,5]

**Explanation:** One possible answer is [0,-3,9,-10,null,5], which represents the shown height balanced BST.

**Example 2:**

**Input:** head = []

**Output:** []

**Constraints:**

- The number of nodes in
`head`

is in the range`[0, 2 * 104]`

. `-105 <= Node.val <= 105`