Pinterest·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Pinterest coding screen for a software engineer role. One question, but it had enough edge cases to keep me busy for the whole session.

Questions Asked (1)

You have a class with a next() method that returns chunks of a string one at a time. The chunks may contain a two-character newline delimiter that can be split across consecutive chunks. Write a function that reads until the stream is exhausted and reconstructs the original lines correctly.

Algorithms & Data StructuresTechnical Trade-offsSystem Design

Author's notes

The split-delimiter case is what got me at first.

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AI HintsAI Generated

Suggested Approach

Use a buffer to accumulate incoming chunks and scan for the newline delimiter, handling cases where the delimiter is split across chunk boundaries. After processing each chunk, emit complete lines and retain any partial line or trailing delimiter character in the buffer for the next iteration. Continue until the stream is exhausted, then flush any remaining buffered content as the final line.

Pro tip: Clarify upfront whether the delimiter is exactly '\n\n' and whether a trailing newline should produce an empty final line—these edge cases often trip up candidates and show attention to detail.

1. Clarify requirements and edge cases

Ask about the delimiter (e.g., '\n\n'), whether it can appear multiple times, and how to handle trailing delimiters or empty lines. Confirm the expected output format (list of lines).

2. Design a buffering strategy

Maintain a string buffer that holds unprocessed characters. For each chunk, append it to the buffer, then search for the delimiter. This handles splits across chunk boundaries.

3. Process and emit complete lines

While the buffer contains the delimiter, extract the substring before it as a line, remove the delimiter from the buffer, and add the line to the result. Repeat until no delimiter remains.

4. Handle stream exhaustion and flush

After the stream ends, if the buffer is non-empty, treat it as the final line (unless it's an empty string from a trailing delimiter). Return all collected lines.

5. Analyze complexity and trade-offs

Discuss time complexity (O(n) where n is total characters) and space complexity (O(m) for buffer and output). Mention alternative approaches like using a state machine or regex, and their trade-offs.

Key Points to Mention

Buffer management to handle delimiters split across chunk boundaries
Edge cases: empty chunks, delimiter at start/end, consecutive delimiters, trailing newline
Time and space complexity analysis
Choice of data structures (e.g., StringBuilder vs. list of strings) and their performance implications
Testing strategy: unit tests with mocked next() method covering boundary conditions
Potential optimizations: avoid unnecessary string copies, use indexOf with start index

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