LeetCode 35 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

分析：

这里我想到的是层序遍历，同时为了区分层，用两个队列交替的方式遍历。

我不知道这算不算constant space.

/**
 * 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> q1 = new LinkedList<TreeLinkNode>();
        Queue<TreeLinkNode> q2 = new LinkedList<TreeLinkNode>();
        q1.add(root);
        while(q1.size()>0 || q2.size()>0){
            while(q1.size()>0){
                TreeLinkNode temp = q1.remove();
                temp.next = q1.peek();
                if(temp.left != null) q2.add(temp.left);
                if(temp.right != null) q2.add(temp.right);
            }
            
            while(q2.size()>0){
                TreeLinkNode temp = q2.remove();
                temp.next = q2.peek();
                if(temp.left != null) q1.add(temp.left);
                if(temp.right != null) q1.add(temp.right);
            }
        }
    }
}