Art of Codeartofcode
Lesson 13 of 15

43. Design Flash-Sale Ticket Booking (Ticketmaster / IRCTC Tatkal)

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The interview prompt
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43.1 What do you ask first?
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43.2 How big is this, really?
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43.3 What are the doors?
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43.4 What do we store?
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43.5 What does the whole system look like?
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43.6 How does the waiting room work?
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43.7 How does seat locking work?
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43.8 How do you rate-limit bots?
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43.9 How do you keep it fair?
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43.10 What would you say in the last five minutes?
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Score yourself
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Variations to practise
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Sources
15
Code lab
43. Design Flash-Sale Ticket Booking (Ticketmaster / IRCTC Tatkal)

Variations to practise

3 min read+10 XP

Chapters used

Approach (1), Estimation (2), Caching (12, 13), Transactions and seat holds (17), Message queues and backpressure (22), Idempotency (24), Rate limiting and bots (25), CDNs (26), Live-event pre-scaling (41), Checkout and payments (42).

Try these variations

Each is a common follow-up. Answer in two minutes, then check the sketch.

  1. "General admission, no seat numbers." → No seat rows: a stock counter per ticket type with conditional decrements (Chapter 42), bucketed if hot.
  2. "Pre-registration lottery." → Accounts register days ahead; a lottery picks winners and assigns time slots; only winners can join the queue in their slot.
  3. "Tatkal: thousands of trains, each with its own quota." → A waiting room per train class or per popular route; holds per berth; quotas per train in separate rows.
  4. "Resale." → Tickets re-listed at a capped price inside the platform; the original ticket is cancelled and a new one issued to the buyer.