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Dandy·Machine Learning Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say
Jun 2026Remote

Summary

Interviewed for an ML Engineer role at Dandy and got a math-heavy technical question that went deeper than I expected. Not a vibe-check round, they actually wanted to talk through edge cases.

Questions Asked (1)

Q1

Given two 3D points, compute the Euclidean distance between them. Then discuss numerical stability issues and how you'd extend the formula to N dimensions.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

Started fine, wrote out the formula no problem.

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AI HintsAI Generated

Suggested Approach

Start by clearly stating the Euclidean distance formula for two 3D points: sqrt((x2-x1)^2 + (y2-y1)^2 + (z2-z1)^2). Then discuss numerical stability issues such as overflow/underflow when squaring large or small numbers, and propose mitigation techniques like scaling or using math.hypot. Finally, generalize to N dimensions by summing squared differences across all dimensions and taking the square root, mentioning efficient computation with vectorization.

Pro tip: Mention that in production ML systems, you'd often use optimized libraries like NumPy or SciPy for distance computations, but understanding the underlying numerical pitfalls is crucial for debugging and for implementing custom kernels.

1. State the 3D Euclidean distance formula

Write the formula explicitly: d = sqrt((x2-x1)^2 + (y2-y1)^2 + (z2-z1)^2). Explain that it's derived from the Pythagorean theorem applied twice.

2. Discuss numerical stability issues

Identify potential problems: overflow when squaring large coordinates, underflow when squaring small differences, and loss of precision when subtracting nearly equal numbers. Mention catastrophic cancellation.

3. Propose stable computation techniques

Suggest scaling coordinates by a common factor before squaring, or using math.hypot which handles overflow/underflow gracefully. For N dimensions, consider using a running sum with compensated summation (Kahan) if needed.

4. Extend to N dimensions

Generalize the formula: d = sqrt(sum_{i=1}^N (p_i - q_i)^2). Explain that the same stability concerns apply, and the computation can be vectorized for efficiency.

5. Relate to ML engineering context

Connect to practical ML use cases: distance metrics in clustering, nearest neighbor search, or loss functions. Mention that libraries like NumPy provide stable implementations, but understanding the math helps in custom implementations.

Key Points to Mention

  • Euclidean distance formula in 3D and its generalization to N dimensions.
  • Numerical stability: overflow, underflow, and catastrophic cancellation when squaring and summing.
  • Mitigation techniques: scaling, math.hypot, compensated summation.
  • Efficiency considerations: vectorization, avoiding loops, using optimized libraries.
  • Relation to ML: distance-based algorithms (k-NN, k-means), similarity metrics, and loss functions.
  • Edge cases: zero distance, high-dimensional spaces (curse of dimensionality), and floating-point precision limits.

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