Implement bitmap font render/compress/invert

Q: Implement bitmap font render/compress/invert

This question evaluates proficiency in bitmap and matrix manipulation, lossless compression/decompression techniques, and modular code reuse for transformations such as inversion, targeting skills in data representation, algorithmic correctness, and space-time trade-offs.

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Coding & Algorithms questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master coding & algorithms interviews.

Q: What difficulty level is this interview question?

This is a medium difficulty Coding & Algorithms question, commonly asked during Take-home Project rounds at Stripe.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Stripe during technical interviews.

Question

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Bitmap Character to Image Conversion (3 phases)

You are given a bitmap lookup table (a dictionary/map) that represents a tiny “font”.

Key : a character (e.g., 'J' )
Value : a 2D grid (matrix) of 0/1 integers where:
- 0 = background pixel
- 1 = foreground pixel

Example bitmap for the letter J (10 rows × 6 columns):

0 0 0 0 1 0
0 0 0 0 1 0
0 0 0 0 1 0
0 0 0 0 1 0
0 0 0 0 1 0
0 0 0 0 1 0
1 0 0 0 1 0
0 1 1 1 0 0
0 0 0 0 0 0
0 0 0 0 0 0

Phase 1: Basic printing

Implement a function that, given the lookup table and an input character, prints the character’s bitmap to the console in the same grid format (preserve rows/columns).

Phase 2: Compression & decompression

To save space, implement:

compress(bitmap) : Convert a 2D 0/1 matrix into a more compact representation.
decompress(compressed) : Restore the original 2D matrix.

Requirements:

The decompressed bitmap must be identical to the original.
After decompressing, print the bitmap again (reuse Phase 1 printing).

Notes:

You may choose any reasonable compression format (e.g., row-wise run-length encoding (RLE), storing coordinates of 1 s, etc.), but it must support lossless round-trip.

Phase 3: Manipulation & reuse

Perform an additional transformation on the bitmap(s), then print the result.

Example transformation: invert the bitmap (swap 0 and 1 ).
You must reuse part of your Phase 2 code (e.g., decompress → manipulate → print, or manipulate compressed data then use existing logic).

Assumptions / clarifications

All bitmaps are rectangular matrices.
Printing can be 0/1 separated by spaces (or equivalent consistent formatting).
The lookup table may contain multiple characters; your functions should work for any entry in the table.