두 갈래 트리 미러링(Leetcode)

problem address
Invert a binary tree.

Example:

Input:

     4
   /   \
  2     7
 / \   / \
1   3 6   9
Output:

     4
   /   \
  7     2
 / \   / \
9   6 3   1
Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.

사고방식은 매우 간단하다. 먼저 뿌리를 두루 훑어보는 복제판은 주로 노드를 찾아 좌우 나무를 맞추면 된다
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def invertTree(self, root: TreeNode) -> TreeNode:
        if root:
            root.left, root.right = root.right, root.left
            self.invertTree(root.left)
            self.invertTree(root.right)
        return root 

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