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. URL: https://leetcode.com/problems/invert-binary-tree/

# 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
        else:
            stack = []
            stack.append(root)
            while stack != []:
                curr_node = stack.pop()
                if curr_node.left != None or curr_node.right != None:
                    temp = curr_node.left
                    curr_node.left = curr_node.right
                    curr_node.right = temp
                if curr_node.right != None:
                    stack.append(curr_node.right)
                if curr_node.left != None:
                    stack.append(curr_node.left)
            return root