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。