Leetcode-Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3
   / 
  9  20
    /  
   15   7

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

Solution:

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        List<Integer> oneRes = new ArrayList<Integer>();
        if (root==null){
            return res;
        }

        List<TreeNode> lastLevel = new ArrayList<TreeNode>();
        lastLevel.add(root);
        oneRes.add(root.val);
        res.add(oneRes);
        List<TreeNode> curLevel;
        while (lastLevel.size()!=0){
            oneRes = new ArrayList<Integer>();
            curLevel = new ArrayList<TreeNode>();
            for (int i=0;i<lastLevel.size();i++){
                TreeNode curNode = lastLevel.get(i);
                if (curNode.left!=null){
                    curLevel.add(curNode.left);
                    oneRes.add(curNode.left.val);
                }
                if (curNode.right!=null){
                    curLevel.add(curNode.right);
                    oneRes.add(curNode.right.val);
                }
            }
            if (curLevel.size()==0){
                break;
            } else {
                res.add(oneRes);
                lastLevel = curLevel;
            }
        }

        return res;        
    }
}