leetcode--二叉樹的層次遍歷

給定一個二叉樹，返回其按層次遍歷的節點值。 （即逐層地，從左到右訪問所有節點）。

例如:
給定二叉樹:?[3,9,20,null,null,15,7],

????3
???/?\
??9??20
????/??\
???15???7

返回其層次遍歷結果：

[
??[3],
??[9,20],
??[15,7]
]

#?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?=?[]
????????cur_node?=?[root]
????????next_node?=?[]
????????res.append([i.val?for?i?in?cur_node])
????????while?cur_node?or?next_node:
????????????for?node?in?cur_node:
????????????????if?node.left:
????????????????????next_node.append(node.left)
????????????????if?node.right:
????????????????????next_node.append(node.right)
????????????if?next_node:
????????????????res.append([
????????????????????i.val?for?i?in?next_node
????????????????])
????????????cur_node?=?next_node
????????????next_node?=?[]
????????return?res

執行用時 :?80 ms, 在Binary Tree Level Order Traversal的Python3提交中擊敗了26.32% 的用戶

內存消耗 :?13.2 MB, 在Binary Tree Level Order Traversal的Python3提交中擊敗了98.08% 的用戶