Populating Next Right Pointers in Each Node II

Description:

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

Code:

 void connect(TreeLinkNode *root) {
        if (!root)
            return ;
        deque<TreeLinkNode*>a;
        deque<TreeLinkNode*>b;
        a.push_back(root);
        
        while (!a.empty())
        {
            while (!a.empty())
            {
                TreeLinkNode* p = a.front();
                a.pop_front();
                if(p->left)
                    b.push_back(p->left);
                if(p->right)
                    b.push_back(p->right);
               
               if (a.empty())  
                    p->next = NULL; 
               else
                    p->next = a.front();
            }
            a = b;
            b.clear();
        }
    }