https://leetcode.cn/problems/invert-binary-tree/ (opens new window) 需要注意的点

1. 递归到子节点， 从子节点开始翻转
2. 翻转节点左右节点，递归处理左节点，然后递归右节点

# 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 invertTree(self, root: TreeNode) -> TreeNode:

        if  not root:
            return root
        
        left  = self.invertTree(root.left)
        right = self.invertTree(root.right)

        root.left = right
        root.right = left

        return root

# 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 invertTree(self, root: TreeNode) -> TreeNode:



        def traverse(node: TreeNode) -> TreeNode:

            if not node:
                return 
            
            tmp = node.right
            node.right = node.left
            node.left = tmp

            traverse(node.left)
            traverse(node.right)
        
        traverse(root)
        return root