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Stripe·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Stripe coding screen for a software engineer role. The problem was more of an implementation exercise than a hard algorithm question, which I did not expect from Stripe.

Questions Asked (1)

Q1

Given a bitfont (a mapping from characters to 2D pixel grids), implement a function that takes a string and returns a single concatenated 2D bitmap of the rendered text, with glyphs laid out left to right.

Algorithms & Data StructuresTechnical Trade-offsAPI & Integrations
Author's notes

Spent the first few minutes overthinking it.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the bitfont representation and edge cases, then outline a simple algorithm: compute total width, create a canvas, and copy each glyph's pixels. Emphasize modularity and testability, and discuss potential optimizations or trade-offs.

Pro tip: Mention that you'd handle missing glyphs gracefully (e.g., skip or use a placeholder) and that you'd consider variable-width fonts, showing attention to real-world robustness.

1. Clarify requirements and assumptions

Ask about the bitfont format (e.g., fixed-width, variable-width, missing characters) and the expected output (e.g., 2D array of bits). Confirm edge cases like empty string or unknown characters.

2. Design the algorithm

Outline steps: compute total width by summing glyph widths, determine height, create a result grid, then iterate through characters and copy each glyph's pixels at the correct offset.

3. Implement with modularity

Write helper functions for getting glyph dimensions and copying pixels. Use clear variable names and handle boundaries to avoid off-by-one errors.

4. Test and validate

Walk through examples (e.g., 'AB', 'A B') and edge cases (empty string, missing glyph). Verify correctness and discuss potential bugs.

5. Discuss trade-offs and extensions

Talk about time/space complexity, possible optimizations (e.g., precomputing widths), and extensions like variable-width fonts or anti-aliasing.

Key Points to Mention

  • Time and space complexity: O(total pixels) time, O(total pixels) space for the output.
  • Handling of missing glyphs: decide whether to skip, use a placeholder, or throw an error.
  • Support for variable-width fonts: compute total width dynamically based on each glyph's width.
  • Edge cases: empty string, single character, characters not in the bitfont.
  • Modularity: separate concerns like glyph lookup, dimension calculation, and pixel copying.
  • Testing strategy: unit tests for typical and edge cases, visual verification if possible.

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