Invert Binary Tree

Invert a binary tree.

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

To

     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 fuck off.

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

class Solution(object):
    def invertTree(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        if root == None:
            return None
        node = TreeNode(root.val)
        node.right = self.invertTree(root.left)
        node.left = self.invertTree(root.right)
        return node