199. 二叉树的右视图 - 力扣（LeetCode）
# 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: Optional[TreeNode]) -> List[int]:
if not root:
return []
queue = deque([root])
result = []
while queue:
level_size = len(queue)
for i in range(level_size):
node = queue.popleft()
# 记录每层的最后一个元素
if i == level_size - 1:
result.append(node.val)
if node.left:
queue.append(node.left)
if node.right:
queue.append(node.right)
return result
