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0110 Balanced Binary Tree

Solved at: 2022-09-25


Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the left and right subtrees of every node differ in height by no more than 1.


# 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 getHeight(self, node):
if node == None:
return 0
l = node.left
r = node.right
return max(self.getHeight(l), self.getHeight(r)) + 1

def isBalanced(self, root: Optional[TreeNode]) -> bool:
if root == None:
return True
l = root.left
r = root.right
lh = self.getHeight(l)
rh = self.getHeight(r)
return abs(lh - rh) <= 1 and self.isBalanced(l) and self.isBalanced(r)



  • 123 ms, faster than14.05%ofPython3online submissions forBalanced Binary Tree.

Memory Usage

  • 18.6 MB, less than90.53%ofPython3online submissions forBalanced Binary Tree.

Complexity Analysis


  • O(nlogn)O(n \log n) because worst case, we might need to travel all nodes while counting their height with O(n)O(n)


  • O(n)O(n) because we require a stack to contain all nodes, worst case.

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