# 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:

if root == None:

return True

if self.ishelp(root) == -1:

return False

else:

return True

def ishelp(self, root):

if root == None:

return 0

if root.left == None and root.right == None:

return 1

left = self.ishelp(root.left)

right = self.ishelp(root.right)

if left == -1 or right == -1:

return -1

if left - right > 1 or right - left > 1:

return -1

else:

return max(left, right) + 1