Populating Next Right Pointers in Each Node II

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

The idea is to use level order traversal, when traversing current level, the current level's next node should be setup already, so we setup next level's next node.

public void connect(TreeLinkNode root) {
        if (root==null){
            return;
        }   

        TreeLinkNode current=root;
        TreeLinkNode nextLevelHead=null;
        TreeLinkNode nextLevelEnd=null;
        while (current!=null) {
            if (current.left!=null){
                if (nextLevelHead==null) {
                   nextLevelHead=current.left;
                   nextLevelEnd=nextLevelHead;
                } else {
                    nextLevelEnd.next=current.left;
                    nextLevelEnd=nextLevelEnd.next;

                }
            }

            if (current.right!=null) {
                if (nextLevelHead==null) {
                   nextLevelHead=current.right;
                   nextLevelEnd=nextLevelHead;
                } else {
                    nextLevelEnd.next=current.right;
                    nextLevelEnd=nextLevelEnd.next;

                }
            }

            current=current.next;
            if (current==null) {                
                current=nextLevelHead;
                nextLevelHead=null;
                nextLevelEnd=null;
            }
        }
    }