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

 

Given an integer array nums where the elements are sorted in ascending order, convert it to a 

height-balanced

 binary search tree.

 

Example 1:

Input: nums = [-10,-3,0,5,9]
Output: [0,-3,9,-10,null,5]
Explanation: [0,-10,5,null,-3,null,9] is also accepted:

Example 2:

Input: nums = [1,3]
Output: [3,1]
Explanation: [1,null,3] and [3,1] are both height-balanced BSTs.

 

Constraints:

• 1 <= nums.length <= 104
• -104 <= nums[i] <= 104
• nums is sorted in a strictly increasing order.

 

 

# 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]) -> Optional[TreeNode]:
        if not nums:
            return None 
        
        mid = len(nums) // 2 

        node = TreeNode(nums[mid])
        node.left = self.sortedArrayToBST(nums[:mid])
        node.right = self.sortedArrayToBST(nums[mid+1:])

        return node