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Binary Tree Level Order Traversal
MediumData StructuresDescription
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).
**Note:** The tree is represented as an array in level-order (BFS) format, where `null` represents missing nodes. Return a 2D array where each inner array contains the values at that level.
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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