199. 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].

Credits:Special thanks to @amrsaqr for adding this problem and creating all test cases.

解题思路

见程序注释