1 """
2 层次遍历
3 """
4 """
5 Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).
6 For example:
7 Given binary tree [3,9,20,null,null,15,7],
8 3
9 / \
10 9 20
11 / \
12 15 7
13 return its bottom-up level order traversal as:
14 [
15 [15,7],
16 [9,20],
17 [3]
18 ]
19 """
20
21 class TreeNode:
22 def __init__(self, x):
23 self.val = x
24 self.left = None
25 self.right = None
26
27 class Solution:
28 def levelOrderBottom(self, root):
29 if root == None:
30 return []
31 queue = []
32 res = []
33 queue.append(root)
34 while queue:
35 n = len(queue) #!!!记录每一层有几个结点
36 newqueue = [] #存储当前层
37 for _ in range(n):
38 x = queue.pop(0) #pop()弹出最后一个元素, pop(0)弹出第一个元素
39 newqueue.append(x.val) #bug newqueue.append(x),这里只存值就可以了
40 if x.left:
41 queue.append(x.left)
42 if x.right:
43 queue.append(x.right)
44 #bug wrong answer res.append(newqueue)
45 res.insert(0,newqueue) #插入到尾部
46 #aList = [123, 'xyz', 'zara', 'abc']
47 #aList.insert( 3, 2009) (索引,数值)
48 #[123, 'xyz', 'zara', 2009, 'abc']
49 return res
