題目

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]
]

myanswer:

只需在102. Binary Tree Level Order Traversal改動一行即可

class Solution:def levelOrderBottom(self, root):""":type root: TreeNode:rtype: List[List[int]]"""if not root:return []res, level = [],[root]while level:currentNode = []nextLevel = []for node in level:currentNode.append(node.val)if node.left:nextLevel.append(node.left)if node.right:nextLevel.append(node.right)res.insert(0, currentNode)   # 每次都給插入到列表的頭部level = nextLevelreturn res

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