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