[leetcode] 226. Invert Binary Tree 解题报告

题目链接：https://leetcode.com/problems/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.

思路：这题有个故事，说是Max Howell去google面试，Max Howell是很有名的软件HomeBrew的作者，然后面试官本想放水，出了一道最简单的题目，谁知大神根本没get到面试官的良苦用心，居然这么不给面子的没做出来！然后完了还在推特上吐槽，引发了各种讨论。在本题的讨论区里各种恶搞，来看有个：

如果你A了这题，你就已经超过了顶级的程序员。

不管你信不信，反正我是信了。

代码如下：

/**
 * 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) return NULL;
        TreeNode* tem = root->left;
        root->left = root->right;
        root->right = tem;
        invertTree(root->left);
        invertTree(root->right);
        
        return root;
    }
};