Binary Tree Right Side View

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.
For example:
Given the following binary tree,

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

You should return [1, 3, 4].


Naive Way: Use a level-order traversal and always note down the last TreeNode value in the result.

 /**  
  * Definition for binary tree  
  * public class TreeNode {  
  *   int val;  
  *   TreeNode left;  
  *   TreeNode right;  
  *   TreeNode(int x) { val = x; }  
  * }  
  */  
 public class Solution {  
   public List<Integer> rightSideView(TreeNode root) {  
     List<Integer> list = new ArrayList<Integer>();  
     List<TreeNode> cur_layer = new ArrayList<TreeNode>();  
     // edge case  
     if(root==null) return list;  
     // initialize current layer  
     cur_layer.add(root);  
     // level-order traversal  
     while(!cur_layer.isEmpty()){  
       list.add(cur_layer.get(cur_layer.size()-1).val);  
       List<TreeNode> next_layer = new ArrayList<TreeNode>();  
       for(TreeNode node: cur_layer){  
         if(node.left!=null) next_layer.add(node.left);  
         if(node.right!=null) next_layer.add(node.right);  
       }  
       cur_layer = next_layer;  
     }  
     return list;  
   }  
 }