Leetcode 199 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]

.

BFS 每层都以从右向左的顺序扔数组里取出第一个到结果数组中，然后再对下一层同样操作。

class Solution(object):
def rightSideView(self, root):
if not root:
return []
a, ans = [root], []
while a:
b = []
ans.append(a[0].val)
for node in a:
if node.right:
b.append(node.right)
if node.left:
b.append(node.left)
a = b
return ans