思路：

判斷是否是平衡二叉樹，即判斷任何一個節點的左子樹和右子樹的高度差的絕對值小於等於1。最直接的做法，遍歷每個結點，藉助一個獲取樹深度的遞迴函式，根據該結點的左右子樹高度差判斷是否平衡，然後遞迴地對左右子樹進行判斷。

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def IsBalanced_Solution(self, pRoot):
        # write code here
        if pRoot == None:
            return True
        if abs(self.TreeDepth(pRoot.left)-self.TreeDepth(pRoot.right)) > 1:
            return False
        return self.IsBalanced_Solution(pRoot.left) and self.IsBalanced_Solution(pRoot.right)
       
    def TreeDepth(self, pRoot):
        # write code here
        if pRoot == None:
            return 0
        nLeft = self.TreeDepth(pRoot.left)
        nRight = self.TreeDepth(pRoot.right)
        return max(nLeft+1,nRight+1)