题解 | #二叉树的镜像#

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param pRoot TreeNode类 
# @return TreeNode类
#
class Solution:
    def Mirror(self , pRoot: TreeNode) -> TreeNode:
        # 如果根节点为空，直接返回
        if pRoot is None:
            return pRoot
            
        # 调用递归函数交换左右子树
        self.change_lf(pRoot)
        return pRoot

    def change_lf(self, pRoot: TreeNode):
        # 如果当前节点为空，返回
        if pRoot is None:
            return 
        
        # 先交换左右子树，再递归处理子节点
        pRoot.left, pRoot.right = pRoot.right, pRoot.left
        
        # 递归处理左子树
        self.change_lf(pRoot.left)
        # 递归处理右子树
        self.change_lf(pRoot.right)