Binary Tree Level-wise Traversal

Problem Statement

Given a binary tree, produce the level-wise traversal of its node values. That is, return the values of nodes grouped by each level, from left to right.

For instance, consider the binary tree represented as [5,3,8,null,null,7,10]:

    5
   / \
  3   8
     /  \
    7    10

Your task is to return the values grouped by levels as follows:

[
  [5],
  [3, 8],
  [7, 10]
]

Examples

// Example 1:
Input: root = [1, 2, 3, 4, 5, null, 7]
Output:
[
  [1],
  [2, 3],
  [4, 5, 7]
]

// Example 2:
Input: root = [10]
Output:
[
  [10]
]

// Example 3:
Input: root = []
Output:
[]

Constraints

• The number of nodes in the tree is between 0 and 1500.
• Node values lie within the range -1000 to 1000.