226. Invert Binary Tree刷题笔记

翻转二叉树，是个梗题了。Max Howell因为做不出这道题被google拒了

# 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: Optional[TreeNode]) -> Optional[TreeNode]:
        if not root:
            return None
        root.left,root.right = root.right,root.left
        self.invertTree(root.left)
        self.invertTree(root.right)
        return root