Leetcode: Invert Binary Tree

Question

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.

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Analysis

Solution

[code]# 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
        """
        return self.helper(root)

    def helper(self, root):
        if root==None:
            return None

        temp1 = self.helper(root.right)
        temp2 = self. helper(root.left)
        root.left = temp1
        root.right = temp2

        return root