/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
struct TreeNode* invertTree(struct TreeNode* root) 
{
    if(NULL == root)
        return NULL;
    
    struct TreeNode* tmp = root->left;

    root->left = invertTree(root->right);
    /*root->left改变,tmp保存root->left原有的值*/
    root->right = invertTree(tmp);
    
    return root;
}