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).
For example:
Given binary tree [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
return its bottom-up level order traversal as:
[ [15,7], [9,20], [3] ]
Python
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def __init__(self):
self.temp_result = dict()
self.result = list()
self.level = 0
def levelOrderBottom(self, root):
"""
:type root: TreeNode
:rtype: List[List[int]]
"""
if root:
self.return_node([root])
for i in range(0,len(self.temp_result)):
self.result.append(self.temp_result[i])
return self.result[::-1]
else:
return []
def return_node(self, root_list):
if root_list:
temp_list = []
for i in root_list:
temp_list.append(i.val)
self.temp_result[self.level] = temp_list
self.level += 1
new_root_list = list()
for i in root_list:
if i:
if i.left:
new_root_list.append(i.left)
if i.right:
new_root_list.append(i.right)
print(new_root_list)
return self.return_node(new_root_list)
return