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Duolingo Machine Learning Engineer Interview Questions

The questions to prepare for a Duolingo Machine Learning Engineer interview. Questions from real interview reports rank first. Updated weekly.

Feature Selection for Supervised Models
Medium

Explain a practical feature selection process using validation, regularization, and model-based importance to improve generalization.

Cross-ValidationFeature EngineeringRegularization
Duolingo
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Optimizing Sorting for Large Datasets
Medium

Explain how to choose and optimize sorting approaches for large datasets based on memory, data distribution, and stability requirements.

ArraysSortingGreedy
Duolingo
Coding Practice Problem
Medium

Tests general programming skills and problem-solving under interview constraints.

Hash TablesDynamic ProgrammingArrays
Duolingo
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Design a Personalized Product Recommender
Hard

Design an end-to-end product recommendation system for a large e-commerce marketplace with strict latency and freshness needs.

Feature StoreFeature DriftModel Serving
Duolingo
Predicting Language Proficiency
Hard

Tests end-to-end system thinking for modeling proficiency from interaction signals.

ML RankingFeature StoreRecommendation Systems
Duolingo
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Designing a Duolingo A/B Test
Medium

Tests experimental design, metrics, and decision-making for product changes at Duolingo.

Hypothesis TestingStatistical SignificanceA/B Testing
Duolingo

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