102. 二叉树的层序遍历 - 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
from collections import deque
class Solution:def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:if not root:return []result = []queue = deque([root])while queue:level_size = len(queue)level_nodes = []for _ in range(level_size):node = queue.popleft()level_nodes.append(node.val)if node.left:queue.append(node.left)if node.right:queue.append(node.right)result.append(level_nodes)return result