LeetCode/0226-Invert-Binary-Tree.py at master · nirmalnishant645/LeetCode · GitHub

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'''
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.
'''
# 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 invertTree(self, root: TreeNode) -> TreeNode:
        if not root:
            return None
        queue = []
        queue.append(root)
        while queue:
            cur = queue.pop(0)
            cur.left, cur.right = cur.right, cur.left
            if cur.left:
                queue.append(cur.left)
            if cur.right:
                queue.append(cur.right)
        return root