You’re interviewing for a backend or data engineering role at a FAANG-level company. The interviewer describes a real product scenario:
A large-scale platform organizes hierarchical data such as user permissions, category trees, service dependencies, or UI components using binary trees.
For analytics dashboards, UI rendering, and monitoring tools, the platform often needs to process the tree level by level, starting from the root and moving downward. This traversal helps visualize hierarchy depth, process nodes by priority, and perform breadth-based computations.
The platform needs a reliable way to traverse a binary tree in level order, collecting node values layer by layer.
This is a common practice coding problem for DSA question might ask in Google, Amazon, Netflix, Meta, Apple, Microsoft, Uber, and Bloomberg interviews.
Your Task
Given the root of a binary tree, return the level order traversal of its node values.
Level order traversal means visiting nodes from left to right at each depth level, starting from the root.
Input Format
root: the root node of a binary tree
Each node is defined as:
TreeNode { int val; TreeNode left; TreeNode right; }
Output Format
- A list of lists of integers
- Each inner list contains the values of nodes at the same depth level
Examples
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: []