199. 二叉树的右视图

思路：二叉树的层次遍历+同深度最后一个元素

# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def rightSideView(self, root: TreeNode) -> List[int]:
'''
思路：
层次遍历+只返回同深度的最后一个元素
'''
res = []
if not root:
return res
q = [root]
while q:
tem = []
length = len(q)
for _ in range(length):
node = q.pop(0)
tem.append(node.val)
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
res.append(tem[-1])
return res