Convert Sorted Array to Binary Search Tree.py

'''

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
'''

# 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
        """
        
        return self.build(nums, 0, len(nums) - 1)
    
    def build(self, nums, left, right):
        if left > right:
            return None
        
        mid = (left + right) // 2
        root = TreeNode(nums[mid])
        root.left = self.build(nums, left, mid - 1)
        root.right = self.build(nums, mid + 1, right)
        
        return root