题目描述

解题思路

就是一个简单的循环，不用递归

# 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]]:
        res_all=[]
        if root is None:
            return []
        nodeList=[root]
        while True:
            if nodeList==[]:
                break 
            tmp=[]
            res=[]
            for node in nodeList:
                res.append(node.val)
                if node.left is not None:
                    tmp.append(node.left)
                if node.right is not None:
                    tmp.append(node.right)
            res_all.append(res)
            del res
            nodeList=tmp
            del tmp
  

        return res_all