We could use DFS and compare height of left subtree and right subtree for each node.
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def isBalanced(self, root: TreeNode) -> bool:
self.balanced = True
self._helper(root)
return self.balanced
def _helper(self, node):
if node is None:
return 0
l = self._helper(node.left)
r = self._helper(node.right)
if abs(l - r) > 1:
self.balanced = False
return max(l, r) + 1