Databricks Interview Questions — Page 16

Databricks·Software Engineer·Technical Phone Screen

Jun 2026

Databricks coding round with a twist on a problem I thought I knew cold. They took the classic encode/decode strings question and made it streaming, which completely changed the complexity.

Implement a streaming variant of the encode/decode strings problem: design an incremental encoder that emits encoded bytes as each string arrives using length-prefixed framing, and a decoder that reads from a byte stream and yields each complete string as soon as it can, handling partial frames and buffer state across calls.

“I knew the static version well enough but the streaming constraint broke my mental model pretty fast.”

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Databricks·Software Engineer·Onsite - Coding / Algorithms

Jun 2026

Databricks software engineer interview with a coding round focused on game engine design. The problem was deceptively layered once they started asking about extensions and edge cases.

Design a Tic-Tac-Toe engine for an n x n board. Implement a move(row, col, player) function that returns whether the move is invalid, results in no winner yet, or declares a winner. Aim for O(1) time per move and O(n) space.
Extend the Tic-Tac-Toe API to support a reset() method and an optional undo() operation.
Write comprehensive tests for the Tic-Tac-Toe engine covering edge cases like repeated moves on the same cell, out-of-bounds inputs, early wins before the board fills, and a completely filled board with no winner.

“I got the basic win-check logic down pretty fast using row/col/diagonal counters per player, which is the standard trick.”

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Databricks·Software Engineer·Onsite - System Design / Architecture

Jun 2026

Databricks system design round focused entirely on a song list class, which sounds deceptively simple until you're 20 minutes deep into debating skip lists versus ordered maps and second-guessing every trade-off you mentioned.

Design a song list class that supports adding a song, removing a song, and reordering the list. Walk through multiple data structure options and justify your choice.

“I went straight to arrays and linked lists like most people probably do, but the interviewer kept pushing on reorder cost.”

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Databricks·Machine Learning Engineer·Onsite - System Design / Architecture

Jun 2026

Databricks ML Engineer interview focused entirely on designing a content moderation system for LLM outputs. One big open-ended system design question that touched everything from modeling choices to serving infrastructure to eval. Pretty intense scope for a single session.

Design an ML system that detects harmful content in LLM-generated outputs, covering categories like hate speech, violence, sexual content, self-harm, and prompt injection. Walk through your full approach from requirements to serving to evaluation.

“This question has a lot of surface area and I think I underestimated how much they wanted me to go deep on the modeling tradeoffs vs.”

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Databricks·Software Engineer·Technical Phone Screen

Jun 2026

Databricks software engineering interview with a tree path problem that looks deceptively clean on the surface but gets tricky fast once you realize you can't just build the tree explicitly.

You have a recursively defined binary tree where T(k) has a root, a left subtree T(k-1), and a right subtree T(k-2), with base cases T(0) and T(1) each being a single node. Nodes are labeled 0 to N-1 in preorder. Given an order, a start node, and an end node, return the unique path between them using only arithmetic, no explicit tree construction.

“The preorder labeling part clicked pretty quickly for me, size(k) follows a Fibonacci-like recurrence so you can compute any subtree's size and figure out whether a given label lives in the left or right subtree.”

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Databricks·Software Engineer·Technical Phone Screen

Jun 2026

Databricks full-stack round that was basically a BFS deep dive. One problem, lots of follow-ups, and they really wanted to see if you'd handle every weird edge case without being prompted.

Given a matrix representing a graph with cells in different states (open, blocked, special), implement BFS to answer reachability or shortest-path queries. Handle edge cases like empty matrix, single-cell input, all cells blocked, start equals target, and multiple disconnected components. Also discuss time and space complexity.

“I got the core BFS down pretty fast but then they just kept adding cases.”

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Databricks·Software Engineer·Onsite - System Design / Architecture

Jun 2026

System design round at Databricks focused entirely on building a game shop service. The depth they wanted on failure scenarios and idempotency was more than I expected for what seemed like a scoped problem.

Design a game shop service that supports adding credit to a user account, purchasing items, and processing refunds. Walk through your API design, database schema, and the core flows.
For the purchase API, should it accept item quantity or total value as input? What are the tradeoffs?
How do you handle duplicate purchase requests caused by client retries? Walk through your idempotency key design.
How would you use database transactions to keep credit balance updates and inventory changes atomic during a purchase?
Walk through the refund flow. What state transitions are involved and what can go wrong?

“I started with the happy path which was probably the wrong move.”

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Databricks·Software Engineer·Onsite - System Design / Architecture

Jun 2026

Databricks system design round focused on building an IP rule matcher from scratch. The depth of the follow-ups was a lot more than I expected for a single problem.

Design and implement an IP rule matcher that returns 'accept' or 'deny' for a given IPv4 address. Rules can be numeric ranges [start, end] or CIDR blocks. Define data structures for addRule, removeRule, and query operations.
How do you resolve overlapping or conflicting rules, for example if a specific CIDR block says 'deny' but a wider range says 'accept'?
What are the time and space complexity trade-offs for supporting up to 100,000 rules with low-latency queries?
Compare data structures for efficient IP range and prefix lookups: interval tree, segment tree, sorted disjoint intervals with binary search, ordered map, and binary or radix trie. What are the trade-offs for static versus dynamic rule sets?
How would you write tests to catch bitwise operator-precedence bugs when parsing and comparing IPv4 addresses?

“I started with a sorted list of intervals and binary search, which felt reasonable, but then they pushed on dynamic updates and my removeRule logic got messy fast.”

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Databricks·Software Engineer·Technical Phone Screen

Jun 2026

Databricks SWE interview with a networking/systems problem that had more layers to it than I expected. The core question was manageable but the follow-ups kept coming and I felt like I was scrambling by the end.

You're given an ordered list of firewall rules in CIDR notation, each marked allow or deny. Given an IP address as input, determine whether it's allowed or blocked. First matching rule wins.
What test cases would you write for this firewall rule lookup?
How would you extend the solution to accept a CIDR block as input instead of a single IP address?
Write pseudocode for the IP lookup against the firewall rule list.

“The base case wasn't bad.”

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Databricks·Software Engineer·Technical Phone Screen

Jun 2026

Databricks SWE interview that went pretty deep into tree recursion, specifically around Fibonacci trees. Not your typical LeetCode grind, this one actually made me think about structural properties rather than just pattern matching.

Given the in-order traversal of a Fibonacci tree of unknown order n, reconstruct the original tree. Explain how the recursive size relationship between the left and right subtrees lets you locate the root, then describe your algorithm and analyze its complexity.

“The key insight is that F(n) has F(n-1) nodes in the left subtree and F(n-2) in the right, so if you know the total size you can figure out the split point and recursively reconstruct.”

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