107二叉树的层序遍历2

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我是靠谱客的博主狂野外套，这篇文章主要介绍107二叉树的层序遍历2，现在分享给大家，希望可以做个参考。

107二叉树的层序遍历2

给你二叉树的根节点 root ，返回其节点值 自底向上的层序遍历 。（即按从叶子节点所在层到根节点所在的层，逐层从左向右遍历）。

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输入：root = [3,9,20,null,null,15,7]
输出：[[15,7],[9,20],[3]]

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输入：root = [1]
输出：[[1]]

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输入：root = []
输出：[]

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# 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: Optional[TreeNode]) -> List[List[int]]:
        #非递归
        results = []
        if not root:return results
        from collections import deque
        que = deque([root])
        while que:
            result = []
            for i in range(len(que)):              
                cur = que.popleft()
                result.append(cur.val)
                if cur.left:
                    que.append(cur.left)
                if cur.right:
                    que.append(cur.right)
            results.append(result)
        return results[::-1]
        #递归 
        # res = []
        # if not root:return []
        # def helper(root, depth):
        #     if len(res) == depth:res.append([])
        #     res[depth].append(root.val)
        #     if root.left:
        #         helper(root.left, depth+1)
        #     if root.right:
        #         helper(root.right,depth+1)   
        # helper(root, 0)
        # return res[::-1]

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# 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: Optional[TreeNode]) -> List[List[int]]:
        #非递归
        results = []
        if not root:return results
        from collections import deque
        que = deque([root])
        while que:
            result = []
            for i in range(len(que)):              
                cur = que.popleft()
                result.append(cur.val)
                if cur.left:
                    que.append(cur.left)
                if cur.right:
                    que.append(cur.right)
            results.append(result)
        return results[::-1]
        #递归 
        # res = []
        # if not root:return []
        # def helper(root, depth):
        #     if len(res) == depth:res.append([])
        #     res[depth].append(root.val)
        #     if root.left:
        #         helper(root.left, depth+1)
        #     if root.right:
        #         helper(root.right,depth+1)   
        # helper(root, 0)
        # return res[::-1]