【leetcode】102. 二叉树的层序遍历（python）

# 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 levelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root:
            return []
        que = [root]
        res = [[root.val]]
        while que:
            tmp = []
            for _ in range(len(que)):
                node = que.pop(0)
                if node.left:
                    que.append(node.left)
                    tmp.append(node.left.val)
                if node.right:
                    que.append(node.right)
                    tmp.append(node.right.val)
            if tmp:
                res.append(tmp)
        return res