Applied intuition·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Applied Intuition SWE interview with a geometry problem that sounds deceptively simple until you're actually in it. The interviewer wanted every edge case handled, and I mean every single one.

Questions Asked (1)

Given two 2D line segments, determine whether they intersect. You must handle edge cases including collinear segments, perpendicular lines, shared endpoints, zero-length segments, and parallel non-collinear segments.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I started with the happy path and the interviewer just kept adding cases.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem and edge cases, then explain the orientation-based method using cross products to determine intersection. Walk through the algorithm step-by-step, covering general cases and special cases like collinear and zero-length segments, and conclude with complexity analysis and potential trade-offs.

Pro tip: Mention that using integer arithmetic for cross products avoids floating-point precision issues, and explicitly handle zero-length segments as points to simplify the logic.

1. Clarify requirements and edge cases

Ask clarifying questions about input format, coordinate ranges, and whether segments are inclusive of endpoints. List all edge cases to handle: collinear, perpendicular, shared endpoints, zero-length, parallel non-collinear.

2. Define orientation and intersection conditions

Explain the orientation function using cross product to determine the relative position of three points. Define the general intersection condition: two segments intersect if the orientations of the endpoints of one segment with respect to the other are different, and vice versa.

3. Handle special cases

For collinear segments, check if the projections overlap. For zero-length segments, treat them as points and check if the point lies on the other segment. For shared endpoints, ensure the intersection is detected.

4. Present algorithm and complexity

Outline the step-by-step algorithm: compute orientations, check general case, then check special cases. State that the time complexity is O(1) and space is O(1).

5. Discuss trade-offs and alternatives

Mention alternative approaches like parametric equations or bounding box checks, and discuss trade-offs such as numerical stability, simplicity, and performance.

Key Points to Mention

Cross product for orientation: sign indicates clockwise, counterclockwise, or collinear.
General intersection condition: orientations differ and points are on opposite sides.
Collinear overlap check: use dot product or coordinate comparison to see if projections overlap.
Zero-length segments: treat as points and check if point lies on the other segment.
Shared endpoints: ensure the algorithm correctly identifies intersection when endpoints coincide.
Integer arithmetic to avoid floating-point errors; complexity O(1).

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