# [Solved] Given the root of a binary tree, return the bottom-up level order traversal of its nodes’ values. (i.e., from left to right, level by level from leaf to root). ## Question

Given the `root` of a binary tree, return the bottom-up level order traversal of its nodes’ values. (i.e., from left to right, level by level from leaf to root).

Example 1:

```Input: root = [3,9,20,null,null,15,7]
Output: [[15,7],[9,20],]
```

Example 2:

```Input: root = 
Output: []
```

Example 3:

```Input: root = []
Output: []
```

Constraints:

• The number of nodes in the tree is in the range `[0, 2000]`.
• `-1000 <= Node.val <= 1000`

## Python Solution

```# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:
if root==None:return[]
q = [root]
res = []
while q:
q_temp = []
re = []
while q:
x = q.pop(0)
re.append(x.val)
if x.left:q_temp.append(x.left)
if x.right:q_temp.append(x.right)
q = q_temp
res.insert(0,re)
return res```
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