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
Source
# 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
def sorted_array_to_BST(nums):
"""recursive approach"""
if not nums:
return None
if len(nums) == 1:
return TreeNode(nums[0])
if length == 2:
return TreeNode(nums[1], TreeNode(nums[0]))
mid = length // 2
return TreeNode(nums[mid], sorted_array_to_BST(nums[:mid]), sorted_array_to_BST(nums[mid+1:]))
def sorted_array_to_BST(nums):
"""alternative version of above solution"""
if not nums:
return None
if len(nums) == 1:
return TreeNode(nums[0])
mid = len(nums)//2
root = TreeNode(nums[mid])
root.left = sorted_array_to_BST(nums[:mid])
root.right = sorted_array_to_BST(nums[mid+1:])
return root