Description
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).
Examples
Input:
root = [3,9,20,null,null,15,7]Output:
[[3],[9,20],[15,7]]Explanation:
Level 0: [3], Level 1: [9,20], Level 2: [15,7]
Input:
root = [1]Output:
[[1]]Explanation:
Single node at level 0.
Input:
root = []Output:
[]Explanation:
Edge case with empty result.
Constraints
- •
The number of nodes in the tree is in the range [0, 2000] - •
-1000 ≤ Node.val ≤ 1000