leetcode108.将有序数组转成二叉搜索树

class Solution:
    def sortedArrayToBST(self, nums: List[int]) -> TreeNode:
        if len(nums) < 1:
            return
        
        length = len(nums)
        index = length // 2
        val = nums[index]
        root = TreeNode(val)

        left = self.sortedArrayToBST(nums[:index])
        right = self.sortedArrayToBST(nums[index+1:])

        root.left = left
        root.right = right

        return root