Binary Tree Right Side View

题目地址：
https://leetcode.com/problems/binary-tree-right-side-view/description/

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].

解题思路：
Foe this problem, we just need to do the bfs and this should be quick.

代码：

public List<Integer> rightSideView(TreeNode root) {
    // assuming that the root is not null    if(root == null){
        return new ArrayList<>();
    }
    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);
    List<Integer> rst = new ArrayList<>();
    while(!queue.isEmpty()){
        int size = queue.size();
        for(int i = 0; i <= size - 1; i++){
            TreeNode node = queue.poll();
            if(i == size - 1){
                rst.add(node.val);
            }
            if(node.left != null){
                queue.offer(node.left);
            }
            if(node.right != null){
                queue.offer(node.right);
            }
        }
    }
    return rst;
}