[LeetCode] 108. Convert Sorted Array to Binary Search Tree

Problem : https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

Use the middle number as the parent node and recursively build the left and right sub-tree.

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sortedArrayToBST(self, nums: List[int]) -> TreeNode:
        
        def helper(left, right):
            if left >= right:
                return None
            
            mid = left + (right - left) // 2
            return TreeNode(nums[mid], helper(left, mid), helper(mid+1, right))
        
        return helper(0, len(nums))

Edited on 07/26/2021. Tidy the code.