108. Convert Sorted Array to Binary Search Tree

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 ofeverynode 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

def sortedArrayToBST(self, nums):
    """
    :type nums: List[int]
    :rtype: TreeNode
    """
    if nums:
        root_index = len(nums)/2
        root = TreeNode(nums[root_index])
        if root_index - 1 >= 0:
            root.left = self.sortedArrayToBST(nums[:root_index])
        if root_index + 1 < len(nums):
            root.right = self.sortedArrayToBST(nums[root_index+1:])
        return root