leetcode笔记：Invert Binary Tree

一. 题目描述

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.

二. 题目分析

题目意图很明显，即翻转一棵二叉树。后面是几句话，大概的意思是：

Google：我们有90%的工程师在使用你写的软件（Homebrew？），但你居然不会在白板上翻转一棵二叉树，真是操蛋。

这是一道任何程序员都应该会的题，递归或者队列迭代解法都可以实现，不多加赘述。

三. 示例代码

// C++，递归
/**
* 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，递归

# Definition for a binary tree node.
# class TreeNode:
#     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 is None:
return None
root.left, root.right = root.right, root.left
self.invertTree(root.left)
self.invertTree(root.right)
return root

四. 小结

该题意在帮助我们复习数据结构的基础。