Leetcode: Convert Sorted Array to Binary Search Tree

Convert Sorted Array to Binary Search Tree

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.


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:

     / \
   -3   9
   /   /
 -10  5

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

## Blog link: https://code.dennyzhang.com/convert-sorted-array-to-binary-search-tree
## Basic Ideas: Find the middle node
## Complexity: Time O(n), Space O(1)

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def sortedArrayToBST(self, nums):
        :type nums: List[int]
        :rtype: TreeNode
        length = len(nums)
        if length == 0:
            return None
        mid_index = length/2
        head = TreeNode(nums[mid_index])
        head.left = self.sortedArrayToBST(nums[0:mid_index])
        head.right = self.sortedArrayToBST(nums[mid_index+1:])
        return head

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