# [107. Binary Tree Level Order Traversal II](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/)

## 题目

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]
]

```
 

## 题目大意

按层序从下到上遍历一颗树。

## 解题思路

用一个队列即可实现。





## 代码

```go

package leetcode

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func levelOrderBottom(root *TreeNode) [][]int {
	tmp := levelOrder(root)
	res := [][]int{}
	for i := len(tmp) - 1; i >= 0; i-- {
		res = append(res, tmp[i])
	}
	return res
}

```