Axon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Axon software engineer interview with a geometry-flavored coding problem. Not the typical graph or DP question I was expecting, which threw me off a bit at first.

Questions Asked (1)

Given a sequence of 2D GPS coordinates representing a recorded path, compress it by removing redundant collinear points. Keep only the endpoints and any points where the direction actually changes, and use integer cross products for the collinearity check to sidestep floating-point issues.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

My first instinct was to just compute slopes between consecutive points and compare them, which is the obvious wrong answer the moment you think about vertical lines or precision loss.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem: we need to remove redundant collinear points from a path while preserving endpoints and direction changes. Explain that collinearity can be checked using the cross product of vectors formed by consecutive points, and that using integer arithmetic avoids floating-point precision issues. Then outline an O(n) algorithm that iterates through the points and keeps only those that are not collinear with their neighbors.

Pro tip: Mention that you would handle edge cases such as duplicate points, paths with fewer than 3 points, and the importance of preserving the original order. Also, note that the cross product sign indicates the direction of the turn, which can be used to detect collinearity.

1. Clarify the problem and constraints

Confirm that the input is a sequence of 2D integer coordinates, and the output should be a compressed sequence preserving the path shape. Ask about edge cases like duplicate points or very short paths.

2. Explain the collinearity check

Describe how to use the cross product of vectors (B-A) and (C-B) to determine if three points A, B, C are collinear. Emphasize that using integer arithmetic avoids floating-point errors.

3. Outline the algorithm

Propose an O(n) single-pass algorithm: initialize a result list with the first point, then for each subsequent point, check if it forms a straight line with the last two points in the result. If not, add it to the result.

4. Discuss edge cases and optimizations

Address handling of duplicate points, paths with fewer than 3 points, and potential memory optimizations. Mention that the algorithm preserves the original order and endpoints.

5. Analyze complexity and trade-offs

State that the time complexity is O(n) and space complexity is O(n) for the output. Discuss trade-offs: integer cross product is exact but may overflow for very large coordinates; consider using larger integer types if needed.

Key Points to Mention

Cross product formula: (B.x - A.x)*(C.y - B.y) - (B.y - A.y)*(C.x - B.x) == 0 for collinearity.
Integer arithmetic avoids floating-point precision issues, ensuring exact collinearity checks.
Single-pass O(n) algorithm with a result list, comparing each new point with the last two kept points.
Edge cases: duplicate points, paths with <3 points, and ensuring endpoints are always kept.
Preservation of direction changes: only remove points where the path goes straight.
Potential integer overflow with large coordinates; use 64-bit integers or arbitrary precision if necessary.

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