[leetcode][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.

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def sortedArrayToBST(self, nums):
        """
        :type nums: List[int]
        :rtype: TreeNode
        """
        if len(nums) == 0:
            return None
        if len(nums) == 1:
            return TreeNode(nums[0])
            
        def insert(nums):
            if len(nums) == 1:
                return TreeNode(nums[0])
            if len(nums) == 0:
                return None
            left = 0
            right = len(nums)
            mid = (left+right)//2
            node = TreeNode(nums[mid])
            node.left = insert(nums[:mid])
            node.right = insert(nums[mid+1:])
            return node
        return insert(nums)