Given the head of a singly linked list where elements are sorted in ascending order, convert it to a height-balanced binary search tree.

  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