
# Problem Definition

## Description

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

For example:
Given binary tree `[3,9,20,null,null,15,7]`,

```plaintext
    3
   / \
  9  20
    /  \
   15   7
```

return its level order traversal as:

```plaintext
[
  [3],
  [9,20],
  [15,7]
]
```

## Notes

1. [YT - Vivekanand Khyade : Algorithm Every Day - Level Order Traversal of a Binary Tree](https://www.youtube.com/watch?v=NjdOhYKjFrU)
1. [YT - Tushar Roy - Coding Made Simple - Level by Level Printing of Binary Tree](https://www.youtube.com/watch?v=7uG0gLDbhsI)
1. [GitHub - Tushar Roy solution](https://github.com/mission-peace/interview/blob/master/src/com/interview/tree/TreeTraversalLevelByLevel.java)