题目：

请完成一个函数，输入一个二叉树，该函数输出它的镜像。
例如输入：
     4
   /   \
  2     7
 / \   / \
1   3 6   9
镜像输出：
     4
   /   \
  7     2
 / \   / \
9   6 3   1
示例 1：
输入：root = [4,2,7,1,3,6,9]
输出：[4,7,2,9,6,3,1]
限制：
0 <= 节点个数 <= 1000

题目的理解：

二叉树思路都是一样的，通过深度进行遍历。

python实现

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def mirrorTree(self, root: TreeNode) -> TreeNode:
        children = list()
        children.append(root)

        while len(children) > 0:
            children_temp = list()

            for child in children:
                if child is not None:
                    node = child.left
                    child.left = child.right
                    child.right = node
                    
                    if child.left is not None:
                        children_temp.append(child.left)
                    
                    if child.right is not None:
                        children_temp.append(child.right)
            
            children = children_temp

        return root