Vanta·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026Remote

Summary

Vanta coding screen for a software engineer role. One meaty implementation question that sounds easy until you start thinking about flags and streaming edge cases.

Questions Asked (1)

Implement the Unix `uniq` command. Given a stream of input lines, collapse adjacent duplicates into one line, and support the -c, -d, and -u flags.

Algorithms & Data StructuresTechnical Trade-offsSystem Design

Author's notes

I got the basic dedup logic pretty fast but then the flags tripped me up more than I expected.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and edge cases, then design a streaming solution that tracks the previous line and a count. Implement the core logic first, then add flag handling for -c, -d, and -u, ensuring correct output formatting. Discuss trade-offs like memory usage and performance, and consider testing with various inputs.

Pro tip: Demonstrate awareness of real-world uniq behavior: it only collapses adjacent duplicates, not all duplicates. Mention that uniq is often used with sort, and that flags can be combined (e.g., -cd).

1. Clarify requirements and edge cases

Ask about input size, whether lines can be empty, and if flags can be combined. Confirm that only adjacent duplicates are collapsed.

2. Design the algorithm

Use a streaming approach: keep the previous line and a count. For each new line, compare with previous; if same, increment count; else, output according to flags and reset.

3. Implement core logic

Write code to read lines, track previous and count, and handle end-of-stream. Ensure correct output for default behavior (print unique lines).

4. Add flag support

Implement -c (prefix count), -d (only duplicates), -u (only unique). Handle combinations and ensure output format matches Unix uniq.

5. Test and discuss trade-offs

Test with edge cases (empty input, all duplicates, no duplicates). Discuss memory (O(1) extra) and time (O(n)) complexity, and potential improvements.

Key Points to Mention

Only adjacent duplicates are collapsed; uniq does not remove all duplicates unless input is sorted.
Streaming algorithm with O(1) extra space (just previous line and count) and O(n) time.
Flag semantics: -c prefixes count, -d prints only duplicate lines, -u prints only unique lines.
Flags can be combined (e.g., -cd prints only duplicates with counts).
Output formatting: count is right-aligned with a tab or spaces, followed by the line.
Edge cases: empty input, single line, lines with no trailing newline, and very long lines.

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