Leetcode Binary Tree Right Side View

题目：

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].

分析：

这道题实际上是分层遍历，但是每层我们只要最后一个节点。

Java代码实现：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List rightSideView(TreeNode root) {
        List result = new ArrayList();
        if(root==null)
            return result;
        result.add(root.val);
        Queue q = new LinkedList();
        if(root.left!=null)
            q.offer(root.left);
        if(root.right!=null)
            q.offer(root.right);
            
        while(!q.isEmpty())
        {
            int size = q.size();
            for(int i=0;i