Binary Tree Tilt

 1 # Definition for a binary tree node.
 2 # class TreeNode(object):
 3 #     def __init__(self, x):
 4 #         self.val = x
 5 #         self.left = None
 6 #         self.right = None
 7 
 8 class Solution(object):
 9     def findTilt(self, root):
10         """
11         :type root: TreeNode
12         :rtype: int
13         """
14         self.sum = 0
15         
16         def abc(root):
17             if not root: return 0
18         
19             left = abc(root.left)
20             right = abc(root.right)
21             self.sum += abs(left - right)
22             return root.val + left + right
23         
24         abc(root)
25         return self.sum