Design a Movie Ticket Booking System (BookMyShow)

The movie ticket booking system (BookMyShow, Fandango, AMC) is the LLD problem that lives or dies on one concurrency question: what happens when two users try to book the same seat at the same instant? Everything else — cities, cinemas, shows, pricing — is conventional modeling. Interviewers ask it precisely because the seat-contention problem is where junior answers fall apart and senior answers shine.

What the interviewer is testing

• Do you immediately identify the double-booking race as the crux, and can you discuss optimistic vs pessimistic locking and a seat-hold TTL as concrete solutions?
• Can you model the hierarchy cleanly — a Movie plays in many Cinemas across Citys; each Cinema has CinemaHalls; a Show is a movie in a hall at a time; a Show has its own Seat instances with status?
• Do you separate pricing (early-bird, weekend, premium-seat) behind a Strategy, booking lifecycle behind a State machine, and payment behind a Factory?
• Do you handle the hold-then-confirm flow: a seat is locked for ~15 minutes while the user pays, then either confirmed or auto-released?

How to frame it

Clarify scope: search shows by city/movie, view a seat map for a show, select seats, hold them, pay, confirm. State the non-functional priority loudly — a seat must never be sold twice, and held-but-unpaid seats must auto-expire so inventory isn't leaked.

Then drive the flow: search → pick show → reserve seats (atomic hold with TTL) → create pending booking → pay → confirm (or expire and release). The worked solution below follows the full 9-section structure and goes deep on locking in section 7.