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
#
# 以根节点为输入，交换左右子树，递归
class Solution:
    def Mirror(self , pRoot: TreeNode) -> TreeNode:
        def exchange(r):
            if not r:
                return None

            if r.left or r.right:
                r.left, r.right = r.right, r.left
            if r.left:
                r.left = exchange(r.left)
            if r.right:
                r.right = exchange(r.right)
            return r
        
        return exchange(pRoot)