分析
用队列存放节点 先进先出每次进入循环时 弹出该层所有节点每次循环末尾 result添加该层节点val列表 # 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]]: result = list() if not root: return [] # 队列 q = list() q.append(root) while q: # 存放该层节点的val order = list() # 该层节点个数 n = len(q) for i in range(n): # 出队列 node = q.pop(0) # 记录该节点val order.append(node.val) if node.left: q.append(node.left) if node.right: q.append(node.right) # 切片 浅拷贝 result.append(order[:]) return result