劍指 Offer 32 - I. 從上到下打印二叉樹(shù)

從上到下打印出二叉樹(shù)的每個(gè)節(jié)點(diǎn)，同一層的節(jié)點(diǎn)按照從左到右的順序打印。

?

例如:

給定二叉樹(shù): [3,9,20,null,null,15,7],

? ? 3

? ?/ \

? 9? 20

? ? /? \

? ?15? ?7

返回：

[3,9,20,15,7]

嗯這個(gè)就是層序遍歷，也就是bfs，熟悉一下python里面queue怎么寫(xiě)~

#?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[int]:

????????if?not?root:return?[]

????????res=[]

????????q=[]

????????q.append(root)

????????while?q:

????????????node=q.pop(0)

????????????res.append(node.val)

????????????if?node.left:

????????????????q.append(node.left)

????????????if?node.right:

????????????????q.append(node.right)

????????return?res