题目描述

blablabla

样例

# 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):
    ans = True
    def isBalanced(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if not root:
            return True
        self.helper(root)
        return self.ans        

    def helper(self, root):
        if not root:
            return 0
        left = self.helper(root.left)
        right = self.helper(root.right)
        if abs(right - left) > 1:
            self.ans = False
        return right + 1 if right > left else left + 1