226. 翻转二叉树

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# 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 swap(self,root,left,right):
        temp = left
        left = right
        right = temp
        root.left,root.right = left,right  # 改变树的结构
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if root == None:
            return root 
        self.swap(root,root.left,root.right) # 改变树的结构
        self.invertTree(root.left)
        self.invertTree(root.right)
        return root