LeetCode--Invert Binary Tree

题目:

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.

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) {}
 * };
 */

    TreeNode* invertTree(TreeNode* root) {
        if(root == NULL)
        {
            return root;
        }
        else
        {
            TreeNode* temp;
            temp = root->left;
            root->left = root->right;
            root->right = temp;
            invertTree(root->left);
            invertTree(root->right);
            return root;
        }  
    }

先将根节点的两个儿子翻转,再递归翻转他们的儿子.