leetcode - Flatten Binary Tree to Linked List

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode * getLastNode(TreeNode *root){
if (root == NULL)
return NULL;
TreeNode * left = root->left, *right = root->right;
root->left = NULL;
root->right = NULL;
TreeNode * link = root;
if (left !=NULL){
root->right = left;
link = getLastNode(left);
}
if (right != NULL){
link->right = right;
link = getLastNode(right);
}
return link;
}
void flatten(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
getLastNode(root);
}
};