binary-tree-level-order-traversal-ii

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Algorithms

Given the <code>root</code> of a binary tree, return the bottom-up level order traversal of its nodes&#39; values. (i.e., from left to right, level by level from leaf to root).

&nbsp;
Example 1:
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/tree1.jpg" style="width: 277px; height: 302px;" />
<pre>
Input: root = [3,9,20,null,null,15,7]
Output: [[15,7],[9,20],[3]]
</pre>

Example 2:

<pre>
Input: root = [1]
Output: [[1]]
</pre>

Example 3:

<pre>
Input: root = []
Output: []
</pre>

&nbsp;
Constraints:

<ul>
	<li>The number of nodes in the tree is in the range <code>[0, 2000]</code>.</li>
	<li><code>-1000 &lt;= Node.val &lt;= 1000</code></li>
</ul>

levelOrderBottom

Binary Tree Level Order Traversal II

Binary Tree Level Order Traversal

binary-tree-level-order-traversal

二叉树的层序遍历

Average of Levels in Binary Tree

average-of-levels-in-binary-tree

二叉树的层平均值

Tree

Breadth-First Search

Binary Tree

给你二叉树的根节点 <code>root</code> ，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）

&nbsp;

示例 1：
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/tree1.jpg" style="width: 277px; height: 302px;" />
<pre>
输入：root = [3,9,20,null,null,15,7]
输出：[[15,7],[9,20],[3]]
</pre>

示例 2：

<pre>
输入：root = [1]
输出：[[1]]
</pre>

示例 3：

<pre>
输入：root = []
输出：[]
</pre>

&nbsp;

提示：

<ul>
	<li>树中节点数目在范围 <code>[0, 2000]</code> 内</li>
	<li><code>-1000 &lt;= Node.val &lt;= 1000</code></li>
</ul>