Practice & Interview
Meta-tips for the OOD round plus open-ended design exercises — ride-sharing and food-delivery prompts that mirror real interview asks.
After working through the patterns and the case studies, the gap to interview readiness is practice under time pressure. The Practice & Interview topic provides the meta-script for the 45-minute round plus two open-ended prompts where you decide on the approach yourself.
The prompts (ride-sharing, food-delivery) are deliberately less-canonical than the headline case studies — interviewers like to test how candidates handle a problem they haven't memorised. Treat them as open exercises: write your own requirements, defend your own choices, time-box yourself.
Key concepts
- Time-box ruthlessly — 5/5/15/10/5/5 is the canonical budget
- Clarify before designing — half the failed interviews are mis-scoped, not mis-designed
- Defend trade-offs out loud — the interviewer wants to hear your reasoning
- Concurrency is always part of the follow-up — pre-prepare a short answer
- Show that you can spot violations of SOLID in your own design as the interviewer pushes
Reference template
// Self-mock-interview ritual
1. Pick a prompt; set a 45-minute timer
2. Spend exactly 5 min on requirements — write them down
3. Draw class diagram on paper, no IDE
4. Pick one flow; sketch its sequence diagram
5. Code one core class — actually compile it
6. Spend the last 5 min critiquing your own design with SOLID lens
7. Write down what went wrong; redo a week laterAdapt to your problem; the structure is the load-bearing part.
Common pitfalls
- Diving into code before drawing a diagram — interviewers want the design conversation
- Defending the first design too long when the interviewer pushes back
- Forgetting to surface non-functional requirements (concurrency, scale, evolvability)
- Practicing only the headline problems — interviewers know which ones are over-prepped
Related topics
Items (3)
- Approaching the OOD Interview
The 45-minute structure: clarify scope, identify entities, draw the class diagram, narrate a flow, defend trade-offs. The meta-script.
Exercise Foundational - Design a Ride-Sharing System
Open-ended exercise — riders, drivers, matching, pricing, surge, trip lifecycle. Scope it like a real interview.
Exercise Intermediate - Design a Food Delivery System
Restaurants, menus, orders, delivery agents, real-time tracking. A multi-actor design with clear failure modes to discuss.
Exercise Intermediate