问题：

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].

解答：

核心思想是每一层只取一个结点，所以result的大小与高度是一样的。

public class Solution {    public void Helper(TreeNode root, List
    
      result, int curLength) {        if (root == null) return;                if (curLength == result.size()) {            result.add(root.val);        }                Helper(root.right, result, curLength + 1);        Helper(root.left, result, curLength + 1);    }        public List
     
       rightSideView(TreeNode root) {        List
      
        result = new ArrayList
       
        ();        Helper(root, result, 0);        return result;    }}