Implement k-means from scratch

Last updated: August 5, 2025

Quick Overview

Write a clean implementation of logistic regression without using ML libraries.

Square/Block
Machine Learning
Data Scientist
Square/Block
August 5, 2025
Data Scientist
Phone Screen
Machine Learning
Medium

26

7

933 solved


Write a clean implementation of logistic regression without using ML libraries.

Machine learning questions at Square/Block test both theoretical understanding and practical experience. This Phone Screen question evaluates your knowledge of ML fundamentals and your ability to apply them to real-world problems.

What the Interviewer Expects
  • Explain the mathematical foundations with clarity
  • Discuss practical implementation considerations and hyperparameter tuning
  • Analyze the technique's strengths and weaknesses for different data types
  • Demonstrate understanding of evaluation methodology and metrics
  • Connect theory to real-world applications with concrete examples
Key Topics to Cover
Model interpretability and explainability
Gradient descent and optimization
Ensemble methods (bagging, boosting, stacking)
Cross-validation and model evaluation
How to Approach This
  1. Understand the bias-variance trade-off. High training accuracy but low test accuracy signals overfitting.
  2. Choose evaluation metrics carefully based on the problem. Accuracy alone is often insufficient.
  3. Feature engineering is often more impactful than model selection.
  4. Know when to use tree-based models (tabular data) vs neural networks (unstructured data).
  5. Handle class imbalance with SMOTE, class weights, or appropriate loss functions.
Possible Follow-up Questions
  • When would you prefer a simpler model over a complex one?
  • How would you handle a highly imbalanced dataset?
  • How would you explain this model's predictions to a non-technical stakeholder?
  • What are the computational costs of this approach at scale?
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Sample Answer
Core Concept: K-Means Clustering

K-means clustering is an unsupervised learning algorithm used to partition a dataset into K distinct clusters based on feature similarity. The core idea is to minimize the variance within each cluster...

How It Works: Mathematical Mechanism

The K-means algorithm follows these steps:

  1. Initialization: Choose K initial centroids randomly from the dataset.
  2. Assignment Step: For each data point, calculate the Euclidean distance to...

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