面试题-04.02-最小高度树

给定一个有序整数数组，元素各不相同且按升序排列，编写一个算法，创建一棵高度最小的二叉搜索树。
示例:
给定有序数组: [-10,-3,0,5,9],
一个可能的答案是：[0,-3,9,-10,null,5]，它可以表示下面这个高度平衡二叉搜索树：

          0 
         / \ 
       -3   9 
       /   / 
     -10  5 

Python3代码：

# 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:
        def helper(nums, left, right):
                if left > right:
                    return None
                mid = left + (right-left)//2
                tn = TreeNode(nums[mid])
                tn.left = helper(nums, left, mid-1)
                tn.right = helper(nums, mid+1, right)
                return tn
        return helper(nums, 0, len(nums) - 1)