Binary Tree Level Order Traversal

Medium · Trees

You are given the root of a binary tree. Group the node values by their depth from the root and return a list of these groups, ordered from the topmost depth down to the deepest, with each group listing the values in left-to-right order at that depth. An empty tree should produce an empty list.

Examples

Input:  root = [3,9,20,null,null,15,7]
Output: [[3],[9,20],[15,7]]
Why:    Node 3 is alone at depth 0, nodes 9 and 20 sit at depth 1, and nodes 15 and 7 sit at depth 2.

Input:  root = [1]
Output: [[1]]
Why:    A single node forms one level containing just itself.

Input:  root = []
Output: []
Why:    An empty tree has no levels at all.

Constraints

0 <= number of nodes <= 2000, -1000 <= Node.val <= 1000

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Practise Binary Tree Level Order Traversal

This statement is written for CodeSpeek. The problem is part of the NeetCode 150 list; Watch NeetCode's explanation of Binary Tree Level Order Traversal. Reference solutions from the NeetCode repository (MIT) are used to verify our tests.