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).
Examples
Example 1
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
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