Leetcode Note: Invert Binary Tree

Leetcode Note: Invert Binary Tree

I. Description

Invert a binary tree.

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

To

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

Trivia:

This problem was too red 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.

Ii. Question Analysis

The intention of the question is obvious, that is, to flip a binary tree. The following is a few words, which roughly mean:

Google: 90% of our engineers are using the software you wrote (Homebrew ?), But you don't actually flip a binary tree on the whiteboard.

This is a question that any programmer should answer. recursive or queue iteration solutions can be implemented without further repeat.

Iii. Sample Code

// C ++, recursive/*** Definition for a binary tree node. * struct TreeNode {* int val; * TreeNode * left; * TreeNode * right; * TreeNode (int x): val (x), left (NULL), right (NULL) {} *}; */class Solution {public: TreeNode * invertTree (TreeNode * root) {if (root = NULL) return root; TreeNode * temp = root-> left; root-> left = root-> right; root-> right = temp; invertTree (root-> left); invertTree (root-> right); return root ;}};

# Python, recursion # Definition for a binary tree node. # class TreeNode: # def _ init _ (self, x): # self. val = x # self. left = None # self. right = Noneclass Solution (object): def invertTree (self, root): "": type root: TreeNode: rtype: TreeNode "if root is None: return None root. left, root. right = root. right, root. left self. invertTree (root. left) self. invertTree (root. right) return root

Iv. Summary

This question is intended to help us review the basics of the data structure.