1. What I learned

    abs()

        It changes a number to an absolute value.

num = -3
print(abs(num))
# 3

2. Code

class Solution:
    def findSumAndTilt(self, node):
        if not node:
            return 0, 0
        left_sum, left_tilt = self.findSumAndTilt(node.left)
        right_sum, right_tilt = self.findSumAndTilt(node.right)
        return node.val+left_sum+right_sum, left_tilt+right_tilt+abs(left_sum-right_sum)

    def findTilt(self, root: TreeNode) -> int:
        return self.findSumAndTilt(root)[1]

3. Result

        Runtime : 40 ms(99.84%), Memory usage : 15.9 MB(72.50%)
        (Runtime can be different by a system even if it is a same code.)

Check out the my GitHub repo for more info on the code. If you have questions, you can leave a reply on this post.