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).
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: []As always, follow the comments for each line.
In this solution, the time complexity is O(n) where “n” is the number of nodes in the tree, and space complexity is O(1).
From my comments on the code, if you have any questions or comments, feel free to reach out.
