Tags: "leetcode", "bst", access_time 1-min read

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Convert Sorted Array to Binary Search Tree

Created: September 14, 2018 by [lek-tin]

Last updated: September 14, 2018

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example

Given the sorted array: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / \
   -3   9
   /   /
 -10  5

Solution

# 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):
        """
        :type nums: List[int]
        :rtype: TreeNode
        """
        if not nums:
            return None

        middle  = len(nums)//2
        new_node = TreeNode(nums[middle])

        new_node.left = self.sortedArrayToBST(nums[:middle])
        new_node.right = self.sortedArrayToBST(nums[middle+1:])
        
        return new_node