Stripe·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

Stripe coding round, one question about bitmap fonts and rendering characters as grids. Niche problem but the core logic isn't too bad once you break it down.

Questions Asked (1)

You're given an array or string of 0s and 1s representing a bitmap font. Write code to render each character as a grid where 0 becomes '.' and 1 becomes '#', and support concatenating multiple characters to print whole words.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The rendering part clicked pretty fast for me, map bits to characters, chunk by row width, done.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying the input format: is the bitmap a 1D array with known width/height, or a string with delimiters? Then design a function that converts each character's bitmap into a grid of '.' and '#', and another function that concatenates multiple character grids horizontally with spacing. Finally, discuss trade-offs like memory usage, handling variable-width characters, and potential optimizations.

Pro tip: Mention that you'd write unit tests for edge cases like empty input, single character, and multiple characters with different widths, and consider how the solution scales if the font size or number of characters grows.

1. Clarify input and output

Ask questions to understand the bitmap representation (e.g., 1D array with width/height, or string with newlines) and the expected output format (e.g., list of strings or printed grid).

2. Design character rendering

Write a function that takes a single character's bitmap and returns a 2D grid (list of strings) where 0 maps to '.' and 1 maps to '#'.

3. Handle concatenation

Write a function that takes multiple character grids and concatenates them horizontally, adding a column of spaces between characters for readability.

4. Discuss trade-offs and optimizations

Talk about memory usage (storing full grids vs. streaming), handling variable-width characters, and potential performance improvements for large inputs.

5. Test and validate

Mention writing tests for edge cases (empty input, single character, multiple characters) and verifying the output visually.

Key Points to Mention

Input parsing: how to interpret the bitmap (e.g., fixed width vs. delimiters).
Mapping 0/1 to '.'/'#' efficiently, possibly using string replace or list comprehension.
Concatenation logic: aligning characters by height and adding spacing.
Handling variable-width characters: need per-character width metadata.
Memory considerations: building full output vs. printing line by line.
Testing edge cases: empty input, single character, multiple characters, and large inputs.

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