# https://leetcode.com/problems/reverse-odd-levels-of-binary-tree
from typing import Optional

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right
class Solution:
    def reverseOddLevels(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        def traverse(left: Optional[TreeNode], right: Optional[TreeNode], depth: int):
            if left is None or right is None:
                return
            if depth % 2 == 1:
                tmp = left.val
                left.val = right.val
                right.val = tmp
            traverse(left.left, right.right, depth + 1)
            traverse(left.right, right.left, depth + 1)
        if root is not None:
            traverse(root.left, root.right, 1)
        return root