838. Level Order Traversal (BFS)

Given the root of a binary tree, return its level-order traversal as a list of levels — each level being a left-to-right list of node values at that depth. Return the result as a nested array. The tree is given as a level-order array with null for missing children.

Input: A level-order array of the tree.

Output: Nested array — values grouped by level.

Examples

Input: [1,2,3,4,5,null,6]
Output: [[1],[2,3],[4,5,6]]
Explanation: Each depth forms one group.

Input: [1]
Output: [[1]]
Explanation: Single level.

Input: []
Output: []
Explanation: Empty tree.

Constraints

• 0<=nodes<=10^4
• -1000<=value<=1000

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