## Problem Statement

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 1.

**Example:**

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

**Solution:**

# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def sortedArrayToBST(self, nums: List[int]) -> TreeNode:
if not nums:
return None
return self._createBST(nums, 0, len(nums)-1)
def _createBST(self, nums, low, high):
if low>high:
return None
mid = low+(high-low)//2
node = TreeNode(nums[mid])
node.left = self._createBST(nums, low, mid-1)
node.right = self._createBST(nums, mid+1, high)
return node