Binary Tree Level Order Traversal
Given the root of a binary tree, return its level-order traversal.
Level-order traversal means visiting the nodes level by level, from left to right.
For example:
3
/ \
9 20
/ \
15 7
The level-order traversal is:
[ [3], [9,20], [15,7] ]
Example 1
Input
root = [3,9,20,null,null,15,7]
Output
[[3],[9,20],[15,7]]
Explanation
The nodes are visited level by level:
Level 1 → 3 L
evel 2 → 9 20
Level 3 → 15 7
Example 2
Input
root = [1]
Output
[[1]]
Explanation
The tree contains only one node.
Constraints
Hints:
Hint 1
Use a queue to process the tree level by level.
Hint 2
First add the root to the queue.
Author & Technical Reviewer
Technically reviewed by: ExamAdda Technical Review Team
Technical Reviewers, ExamAdda
Software engineers at ExamAdda who check every article's definitions, complexity claims and code examples before and after publishing.
Published
Aug 12, 2026
Last updated
Aug 13, 2026
Content Verification Methodology
Definitions and complexity claims were checked against authoritative computer-science references. Code examples were compiled and tested with standard, boundary and edge-case inputs.
Expected Output