INTERVIEW PREPARATION

Interview questions, answered as mechanisms

Practise explaining the mechanism behind each question. Follow the answer to an article or visualiser, then try again in your own words.

Data structures and algorithms

Foundations 4 questions · 4 answered

• BFS or DFS — which one, and why? BFS vs DFS →
• What is the time complexity of binary search, and what has to be true for it to hold? Binary search →
• Why does insertion order change a binary search tree’s cost? Binary search tree visualiser →
• When does a hash table stop being O(1)? Hash tables: keys, collisions and lookup cost →

Databases and persistence

Persistence 3 questions · 3 answered

• B-tree or LSM-tree — how would you choose? B-Tree vs LSM-Tree →
• A PostgreSQL query has an index and is not using it. What do you check? Why PostgreSQL is not using your index →
• How do you make a payment endpoint safe to retry? Idempotency keys and safe retries →

Architecture and system design

Architecture 2 questions · 2 answered

• Where do you put a service boundary, and how do you know? Bounded contexts, concretely →
• Design a rate limiter. Rate limiting →