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Problems

Basics first, then the classics, then company-style assessments. Every problem has tests you run right here; multi-level ones unlock as you go. See the roadmap.

Coordination

Condition variable

wait_for(predicate) + notify_all; always include a termination case.

Quiz (10) Spot the pattern
Notes

Recognise it when: "wait until some predicate over shared state holds": turn-taking, ordering, bounded queues.

cond = threading.Condition()
with cond:
    cond.wait_for(lambda: done or my_turn())   # re-checks after every notify
    if done: return
    ...mutate state...
    cond.notify_all()

Gotchas

  • Every predicate needs an escape clause (done / i > n). Otherwise a waiter whose turn never comes hangs forever (the FizzBuzz TLE).
  • The method runs once per thread, so the loop goes inside it.
  • After changing state, notify_all(). Anyone waiting on a different predicate needs to re-check.

6 problems

Concurrency

Coordination Semaphores, conditions and barriers.

Condition variable

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