leetcode - Invert Binary Tree

/**
 * 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(NULL == root) return root;
        //if(NULL == root->right && NULL == root->left) return root;   这句是没有必要的
        TreeNode* temp = root->right;
        root->right = invertTree(root->left);
        root->left = invertTree(temp);
    }
};