Given an array 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
Given the sorted array: [-10,-3,0,5,9], One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST: 0 / \ -3 9 / / -10 5