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# 102. Binary Tree Level Order Traversal

## Medium

***

Given the `root` of a binary tree, return *the level order traversal of its nodes' values*. (i.e., from left to right, level by level).

 

**Example 1:**

![](https://assets.leetcode.com/uploads/2021/02/19/tree1.jpg)

```
Input: root = [3,9,20,null,null,15,7]
Output: [[3],[9,20],[15,7]]
```

**Example 2:**

```
Input: root = [1]
Output: [[1]]
```

**Example 3:**

```
Input: root = []
Output: []
```

 

**Constraints:**

* The number of nodes in the tree is in the range `[0, 2000]`.
* `-1000 <= Node.val <= 1000`