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Commit d00930e

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‎index-tags.md

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| [100](https://leetcode-cn.com/problems/same-tree) | [相同的树](/solution/100-199/0100.same-tree/) | `树`,`深度优先搜索` | <font color=green>简单</font> |✅ |
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| [101](https://leetcode-cn.com/problems/symmetric-tree) | [对称二叉树](/solution/100-199/0101.symmetric-tree/) | `树`,`深度优先搜索`,`广度优先搜索` | <font color=green>简单</font> |✅ |
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| [104](https://leetcode-cn.com/problems/maximum-depth-of-binary-tree) | [二叉树的最大深度](/solution/100-199/0104.maximum-depth-of-binary-tree/) | `树`,`深度优先搜索` | <font color=green>简单</font> |✅ |
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| [107](https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii) | [二叉树的层次遍历 ii](/solution/100-199/0107.binary-tree-level-order-traversal-ii/) | `树`,`广度优先搜索` | <font color=green>简单</font> |✅ |
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#### **递归**
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| 题号 | 题解 | 标签 | 难度 | 是否解题 |
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| --- | --- | --- | --- | --- |
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| [101](https://leetcode-cn.com/problems/symmetric-tree) | [对称二叉树](/solution/100-199/0101.symmetric-tree/) | `树`,`深度优先搜索`,`广度优先搜索` | <font color=green>简单</font> |✅ |
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| [107](https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii) | [二叉树的层次遍历 ii](/solution/100-199/0107.binary-tree-level-order-traversal-ii/) | `树`,`广度优先搜索` | <font color=green>简单</font> |✅ |
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#### **贪心算法**
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‎index-type.md

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| [100](https://leetcode-cn.com/problems/same-tree) | [相同的树](/solution/100-199/0100.same-tree/) | `树`,`深度优先搜索` | <font color=green>简单</font> |✅ |
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| [101](https://leetcode-cn.com/problems/symmetric-tree) | [对称二叉树](/solution/100-199/0101.symmetric-tree/) | `树`,`深度优先搜索`,`广度优先搜索` | <font color=green>简单</font> |✅ |
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| [104](https://leetcode-cn.com/problems/maximum-depth-of-binary-tree) | [二叉树的最大深度](/solution/100-199/0104.maximum-depth-of-binary-tree/) | `树`,`深度优先搜索` | <font color=green>简单</font> |✅ |
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| [107](https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii) | [二叉树的层次遍历 ii](/solution/100-199/0107.binary-tree-level-order-traversal-ii/) | `树`,`广度优先搜索` | <font color=green>简单</font> |
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| [107](https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii) | [二叉树的层次遍历 ii](/solution/100-199/0107.binary-tree-level-order-traversal-ii/) | `树`,`广度优先搜索` | <font color=green>简单</font> |✅ |
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| [108](https://leetcode-cn.com/problems/convert-sorted-array-to-binary-search-tree) | [将有序数组转换为二叉搜索树](/solution/100-199/0108.convert-sorted-array-to-binary-search-tree/) | `树`,`深度优先搜索` | <font color=green>简单</font> |
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| [110](https://leetcode-cn.com/problems/balanced-binary-tree) | [平衡二叉树](/solution/100-199/0110.balanced-binary-tree/) | `树`,`深度优先搜索` | <font color=green>简单</font> |
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| [111](https://leetcode-cn.com/problems/minimum-depth-of-binary-tree) | [二叉树的最小深度](/solution/100-199/0111.minimum-depth-of-binary-tree/) | `树`,`深度优先搜索`,`广度优先搜索` | <font color=green>简单</font> |
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# [100. xxx](https://leetcode-cn.com/problems/recover-binary-search-tree)
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# [107. 二叉树的层次遍历 II](https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/description/)
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### 题目描述
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<p>给定一个二叉树,返回其节点值自底向上的层次遍历。 (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)</p>
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<p>例如:<br>
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给定二叉树 <code>[3,9,20,null,null,15,7]</code>,</p>
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<pre> 3
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/ \
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9 20
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/ \
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15 7
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</pre>
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<p>返回其自底向上的层次遍历为:</p>
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<pre>[
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[15,7],
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[9,20],
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[3]
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]
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</pre>
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### 解题思路
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1. BFS
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### 具体解法
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<!-- tabs:start -->
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#### **Golang**
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```go
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func levelOrderBottom(root *TreeNode) [][]int {
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var res [][]int
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if root == nil {
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return res
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}
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queue := []*TreeNode{root}
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for len(queue) > 0 {
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l := len(queue)
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list := make([]int, 0)
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for i := 0; i < l; i++ {
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node := queue[i]
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list = append(list, node.Val)
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if node.Left != nil {
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queue = append(queue, node.Left)
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}
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if node.Right != nil {
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queue = append(queue, node.Right)
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}
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}
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res = append([][]int{list}, res...)
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queue = queue[l:]
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}
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return res
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}
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```
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<!-- tabs:end -->
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/*
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* @lc app=leetcode.cn id=107 lang=golang
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*
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* [107] 二叉树的层次遍历 II
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* type TreeNode struct {
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* Val int
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* Left *TreeNode
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* Right *TreeNode
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* }
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*/
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func levelOrderBottom(root *TreeNode) [][]int {
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var res [][]int
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if root == nil {
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return res
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}
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queue := []*TreeNode{root}
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for len(queue) > 0 {
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l := len(queue)
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list := make([]int, 0)
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for i := 0; i < l; i++ {
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node := queue[i]
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list = append(list, node.Val)
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if node.Left != nil {
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queue = append(queue, node.Left)
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}
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if node.Right != nil {
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queue = append(queue, node.Right)
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}
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}
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res = append([][]int{list}, res...)
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queue = queue[l:]
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}
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return res
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}
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// @lc code=end
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‎solution/100-199/_sidebar.md

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- [104. 二叉树的最大深度 ✅](solution/100-199/0104.maximum-depth-of-binary-tree/)
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- [105. 从前序与中序遍历序列构造二叉树](solution/100-199/0105.construct-binary-tree-from-preorder-and-inorder-traversal/)
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- [106. 从中序与后序遍历序列构造二叉树](solution/100-199/0106.construct-binary-tree-from-inorder-and-postorder-traversal/)
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- [107. 二叉树的层次遍历 ii](solution/100-199/0107.binary-tree-level-order-traversal-ii/)
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- [107. 二叉树的层次遍历 ii ✅](solution/100-199/0107.binary-tree-level-order-traversal-ii/)
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- [108. 将有序数组转换为二叉搜索树](solution/100-199/0108.convert-sorted-array-to-binary-search-tree/)
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- [109. 有序链表转换二叉搜索树](solution/100-199/0109.convert-sorted-list-to-binary-search-tree/)
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- [110. 平衡二叉树](solution/100-199/0110.balanced-binary-tree/)

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