求解:两种递归方式的差异?

测试用例[-10,-3,0,5,9],前面是我的写法,返回结果是[]

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
        else:
            middle = len(nums)//2
            root =TreeNode(nums[middle])
            root.left=self.sortedArrayToBST(nums[0:middle])
            root.right=self.sortedArrayToBST(nums[middle+1:len(nums)])

        return root

后面是路人的写法,可以 AC

class Solution:
    def sortedArrayToBST(self, nums):
        """
        :type nums: List[int]
        :rtype: TreeNode
        """
        if not nums:
            return None
        else:
            mid=len(nums)//2
            tn=TreeNode(nums[mid])
            nums1=nums[0:mid]
            nums2=nums[mid+1:len(nums)]
            tn.left=self.sortedArrayToBST(nums1)
            tn.right=self.sortedArrayToBST(nums2)
        return tn

感觉很奇怪啊,不知道为什么