102. Binary Tree Level Order Traversal

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https://leetcode.com/problems/binary-tree-level-order-traversal/description/
二叉树层序遍历
思路：经典的队列问题

复制代码

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# Definition for a binary tree node.
# class TreeNode:
#
def __init__(self, x):
#
self.val = x
#
self.left = None
#
self.right = None
import queue
class Solution:
def levelOrder(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""
if not root:
return []
res = []
q = queue.Queue()
q.put(root)
while q.qsize() > 0:
#队列非空时，每次遍历一层
n = q.qsize()
#该层大小
data = []
#该层数据
for i in range(n):
#遍历该层
node = q.get()
#从队列中取出结点
data.append(node.val)
#记录数据
#左右子入队
if node.left:
q.put(node.left)
if node.right:
q.put(node.right)
res.append(data)
return res