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