Databricks·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026Remote

Summary

Databricks SWE interview with a networking/IP problem that looked simple but required you to actually know how CIDR masks work under the hood. One question, pretty focused, felt more like a technical phone screen than a full onsite loop.

Questions Asked (1)

Given a single IPv4 address and a list of CIDR blocks, return the first CIDR block in the list that contains the given IP address, or null if none match.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I knew what CIDR was conceptually but blanked for a second on how to actually compare the bits programmatically.

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AI HintsAI Generated

Suggested Approach

Clarify the input format and constraints, then propose a solution that converts the IP and CIDR blocks to integers for efficient bitwise comparison. Discuss trade-offs between linear scan and optimized approaches like sorting or using a trie, and handle edge cases such as invalid inputs.

Pro tip: Mention that you would validate the IP and CIDR formats upfront to avoid runtime errors, and consider using a binary search on sorted CIDR blocks for O(log n) lookup if the list is large and static.

1. Clarify requirements and constraints

Ask about input size, whether the list is static or dynamic, and if the CIDR blocks can overlap. Confirm the expected return type and error handling for invalid inputs.

2. Choose data representation

Convert IPv4 addresses and CIDR blocks to 32-bit integers for efficient bitwise operations. For each CIDR, compute the network address and subnet mask.

3. Design the algorithm

For a linear scan, check if (ip & mask) == network for each CIDR. For optimization, sort CIDRs by network address and use binary search, or build a trie for prefix matching.

4. Analyze trade-offs

Compare time and space complexity: linear scan is O(n) time, O(1) space; sorting + binary search is O(n log n) preprocessing, O(log n) query; trie is O(32) query but O(n*32) space.

5. Handle edge cases and test

Consider invalid IP/CIDR, empty list, overlapping CIDRs, and boundary cases like /0 or /32. Walk through a simple example to verify correctness.

Key Points to Mention

Bitwise operations for IP matching: (ip & mask) == network
CIDR notation and subnet mask calculation
Time and space complexity trade-offs between linear scan, sorting, and trie
Handling overlapping CIDR blocks and returning the first match
Input validation and error handling for malformed IPs or CIDRs
Potential for binary search on sorted CIDR blocks for efficient lookup

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.