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Binary Tree Level Order Traversal

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LeetCode 102. Binary Tree Level Order Traversal

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

Example 1

Input:  root = [3,9,20,null,null,15,7]

3 Level 0 / \ 9 20 Level 1 / \ 15 7 Level 2Output: [[3],[9,20],[15,7]]

Example 2

Input:  root = [1]
Output: [[1]]

Example 3

Input:  root = []
Output: []

Constraints

  • The number of nodes in the tree is in the range [0, 2000]
  • -1000 <= Node.val <= 1000

How the tests work: trees are written as level-order arrays — [1,null,2] is a root 1 with a right child 2. Your function receives real TreeNode objects.

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List of test cases (10)
Case 1
root = [3,9,20,null,null,15,7]
Case 2
root = [1]
Case 3
root = []
Case 4
root = [1,2,3,4,5,6,7]
Case 5
root = [1,2,null,3,null,4]
Case 6
root = [1,null,2,null,3,null,4]
Case 7
root = [5,3,8,1,4,7,9]
Case 8
root = [1,2,3]
Case 9
root = [10,5,15,3,7,12,20]
Case 10
root = [1,2,3,4,null,null,5]