leetcode 두 갈래 나무의 층차가python3

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:

        if not root:return []
 
        queue,res = [],[]
        queue.append(root)
 
        while queue:
            cl = []
            for _ in range(len(queue)):
                node = queue.pop(0)
                cl.append(node.val)
                if node.left:queue.append(node.left)
                if node.right:queue.append(node.right)
            res.append(cl)
        return res