LeetCode题解226-Invert Binary Tree（C++）

题目：

Invert a binary tree.

Example:

Input:

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

Output:

     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 f*** off.

思路：递归将左右节点交换

代码：

/**
 * 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:
    //226. Invert Binary Tree
    //递归，将左右节点交换
    TreeNode* invertTree(TreeNode* root) {
        if(root == NULL) return NULL;
        TreeNode* left = root->left;
        TreeNode* right = root->right;
        root->left = right;
        root->right = left;
        invertTree(left);
        invertTree(right);
        return root;
    }
};