563. Binary Tree Tilt

Python

class Solution:
    def __init__(self):
        self.total_tilt = 0

    def findTilt(self, root: Optional[TreeNode]) -> int:
        self._travel(0, root)
        return self.total_tilt

    def _travel(self, total: int, node) -> tuple:
        if not node:
            return 0

        left_total = self._travel(0, node.left)
        right_total = self._travel(0, node.right)

        self.total_tilt += abs(left_total - right_total)

        return node.val + left_total + right_total