Databricks·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Databricks coding round focused on run-length encoding, which sounds like a warmup problem until you actually get into the edge cases and realize there's a lot more to discuss than the basic compress/decompress logic.

Questions Asked (1)

Implement run-length encoding: write an encode function that compresses a string by replacing consecutive identical characters with the character and its count, then write a decode function that reverses it. Be prepared to discuss edge cases like single characters, multi-digit counts, runs exceeding some cap, and input strings that contain digit characters.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I got the basic encode working pretty fast but decode is where things got messy.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the encoding format and edge cases, then implement encode and decode with a single pass each, using a delimiter or escaping to handle digit characters. Discuss trade-offs like run-length cap and multi-digit counts, and test with examples covering all edge cases.

Pro tip: Mention that the encoded format must be unambiguous; propose using a delimiter like '#' or escaping digits to avoid confusion with counts. Also, discuss how to handle runs exceeding a cap by splitting into multiple runs.

1. Clarify requirements and edge cases

Ask about the expected format, whether counts can be multi-digit, if there's a cap on run length, and how to handle digit characters in the input. Confirm if the encoded string should be decodable without ambiguity.

2. Design the encoding format

Decide on a format that unambiguously separates characters and counts, e.g., using a delimiter like '#' or escaping digits. Consider if runs exceeding a cap should be split into multiple runs.

3. Implement encode

Iterate through the string, count consecutive identical characters, and append the character and count to the result. Handle multi-digit counts and ensure the format is consistent.

4. Implement decode

Parse the encoded string by reading a character, then reading the following digits as the count, and appending the character repeated count times. Handle multi-digit counts and delimiters/escapes correctly.

5. Test and discuss trade-offs

Test with edge cases: empty string, single character, runs with multi-digit counts, runs exceeding cap, and strings containing digits. Discuss trade-offs like simplicity vs. robustness, and potential optimizations.

Key Points to Mention

Handling multi-digit counts: ensure the decoder reads all consecutive digits as one number.
Ambiguity with digit characters: use a delimiter or escaping to distinguish counts from characters.
Run-length cap: if a maximum run length is specified, split runs into multiple encoded segments.
Edge cases: empty string, single character, runs of length 1, and strings with digits.
Time and space complexity: O(n) time for both encode and decode, O(n) space for output.
Trade-offs: simplicity of format vs. robustness to arbitrary input; potential for compression ratio.

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