mq005.二叉树的层序遍历

# 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 []
        res, stack = [], [root]
        while stack:
            seg = []
            for i in range(len(stack)):
                tmp = stack.pop(0)
                seg.append(tmp.val)
                if tmp.left:
                    stack.append(tmp.left)
                if tmp.right:
                    stack.append(tmp.right)
            res.append(seg)
        return res