Binary Tree Tilt.py

#!/usr/bin/python

'''
Given the root of a binary tree, return the sum of every tree node's tilt.
The tilt of a tree node is the absolute difference between the sum of all left subtree node values and all right subtree node values. If a node does not have a left child, then the sum of the left subtree node values is treated as 0. The rule is similar if there the node does not have a right child.
'''

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def findTilt(self, root: Optional[TreeNode]) -> int:
        
        def helper(root):
            if not root: 
                return 0
            
            left = helper(root.left)
            right = helper(root.right)
            self.ans += abs(left - right)
            
            return root.val + left + right
        
        self.ans = 0
        helper(root)
        return self.ans