populating-next-right-pointers-in-each-node-ii leetcode C++

Follow up for problem "Populating Next Right Pointers in Each Node".

What if the given tree could be any binary tree? Would your previous solution still work?

Note:

You may only use constant extra space.

For example, Given the following binary tree,

     1
   /  \
  2    3
 / \    \
4   5    7

After calling your function, the tree should look like:

     1 -> NULL
   /  \
  2 -> 3 -> NULL
 / \    \
4-> 5 -> 7 -> NULL

C++

/**
 * Definition for binary tree with next pointer.
 * struct TreeLinkNode {
 *  int val;
 *  TreeLinkNode *left, *right, *next;
 *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
 * };
 */
class Solution {
public:
       void connect(TreeLinkNode *root){
        while(root){
            TreeLinkNode L(-1);
            TreeLinkNode *f;
            TreeLinkNode *p;
            f = &L;
            p = root;
            while(p){
                if(p->left != NULL){
                    f->next = p->left;
                    f = f->next;
                }
                if(p->right != NULL){
                    f->next = p->right;
                    f = f->next;
                }
                p = p->next;
            }
            root = L.next;
        }
    }
};