Populating Next Right Pointers in Each Node II

Q:

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

Solution:

/** * Definition for binary tree with next pointer. * public class TreeLinkNode { *     int val; *     TreeLinkNode left, right, next; *     TreeLinkNode(int x) { val = x; } * } */public class Solution {    public void connect(TreeLinkNode root) {        if (root == null)            return;        Queue<TreeLinkNode> queue = new LinkedList<TreeLinkNode>();        queue.offer(root);        while (!queue.isEmpty()) {            Queue<TreeLinkNode> level = new LinkedList<TreeLinkNode>();            TreeLinkNode first = queue.poll();            if(first.left != null) level.offer(first.left);            if(first.right != null) level.offer(first.right);            while (!queue.isEmpty()) {                TreeLinkNode second = queue.poll();                if(second.left != null) level.offer(second.left);                if(second.right != null) level.offer(second.right);                first.next = second;                first = second;            }            first.next = null;            queue = new LinkedList<TreeLinkNode>(level);        }    }}