Binary Tree Level Order Traversal II

first.py

from collections import deque 
# 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 not root:
            return []
        ans = []
        subans = []
        q = deque()
        root.h = 0
        q.appendleft(root)
        while q:
            e = q.pop()
            if subans and subans[-1].h != e.h:
                ans.insert(0,[el.val for el in subans])
                subans = []
            subans.append(e)
            if e.left:
                e.left.h = e.h + 1
                q.appendleft(e.left)
            if e.right:
                e.right.h = e.h + 1
                q.appendleft(e.right)
        ans.insert(0,[el.val for el in subans])
        return ans