Zeni Study

Pages
- Learn Python In 7 Days
  Day 1 : Variable + if/else
  Day 2: Loops
  Day 3 : Array + String
  Day 4 — Functions
  Day 5 — Dictionaries - Hashmap
  Day 6 — Files & Errors
  Day 7 — Mini Project & Programmer Thinking
- Machine Coding:
  Day 1 — Bank account + Wallet :
  Day 2 : RateLimiter + seat booking
  Day 3 : Library Management + Classroom Attendance System
  Day 4 : Bank account and notification system.
  Day 5 : Key-value and payment processor.
  Day 6 : Discount engine + Seat booking( in depth)
  Day 7: Parking lot System :
- Machine coding extended:
  Day 7.5 — Parking Lot (Constraint-Heavy Variant)
  Day 8 : Order + Payment System
  Day 8 — Extension Round (Mid-Interview Change)
  Day 9 — Ticket Booking with Expiry (Simulated Time)
  Day 9 — Extension Round (Seat Lock Ownership + Forced Unlock)
- SQL + DB Thinking course
  Day 1 — Tables, Rows & Thinking in Data
  Day 2 — Relationships & Foreign Keys (Thinking in Connections)
  Day 3 — Filtering, Aggregation & Answering Data Questions
  Day 4 — JOINs (Combining Tables the Right Way)
  Day 5 — Subqueries, EXISTS & NOT EXISTS (Thinking in Layers)
  Day 6 — Indexes, Constraints & How Databases Think
  Day 7 — Full SQL Interview Simulation (SDE-1 Ready)
  Extended Day 1 — Core Business Systems (Deep Practice)
  Extended Day 2 — Booking & Platform Systems (High-Depth Practice)
  Extended Day 3 — Content & Learning Platforms (Capstone Practice)
- LLD: Java
  DAY 1 — Core Foundations (SDE-2 Level)
  DAY 2 — State, Time & Domain Correctness
  DAY 3 — Extensibility & Failure Handling (SDE-2 Core Signal)
  DAY 4 — Concurrency, Scheduling & Consistency (SDE-2 Critical)
  DAY 5 — Workflow Design & Config-Driven Systems (SDE-2+)
  DAY 6 — Eventing & Usage-Based Systems (Advanced SDE-2)
  DAY 7 — Interview Simulation (Hard, Production-Grade)
  Hidden Edge Cases Interviewers Expect (Day-wise)
  Detailed Testing file:
- Assignment:
  If else Practice Set

Zeni Study

...

Day 9 — Extension Round (Seat Lock Ownership + Forced Unlock)

Explore

Day 9 — Extension Round (Seat Lock Ownership + Forced Unlock)

Perfect. Below is Day 9 — Extension Round, added on top of the base Day 9 (Ticket Booking with Expiry).

This mirrors a real interview move:

“Okay, your basic solution works. Now let’s extend it.”

This extension is hard but fair, still Level-1+, and extremely common in SDE-1 interviews.

⁠

🟢 Day 9 — Extension Round (Seat Lock Ownership + Forced Unlock)

⁠

⏱ Extension Rules (Tell Candidate Clearly)

⏰ Time for extension: 25–30 minutes

❌ Do NOT change existing method signatures

❌ Do NOT break existing Day 9 tests

❌ Do NOT use real time

❌ Do NOT add new public classes

✅ You MAY add new private variables

✅ You MAY add new public methods only if specified

⁠

🧩 Extension Requirement — Lock Ownership

New Business Requirement

Seat locks are now user-specific.

A seat lock belongs to a user

Only the same user can book the seat

Only the same user can unlock before expiry

Expiry unlock works for any user

⁠

🆕 New Concepts Introduced (Still Safe)

Lock ownership

User-based validation

Slightly more state

No new patterns

⁠

🧱 Updated Seat Rules

New Fields (Internal Only)

Seat must now track:

locked_by → user_id (or None)

lock_time (already exists)

⁠

🔄 Updated Behavior Rules

⁠

lock(current_time, user_id)

⚠️ Method signature changes ONLY for this method

def lock(self, current_time: int, user_id: str) -> bool:

Return True if:

Seat is FREE

Then:

State → LOCKED

Store lock_time

Store locked_by = user_id

Else return False.

⁠

book(current_time, user_id)

⚠️ Method signature changes ONLY for this method

def book(self, current_time: int, user_id: str) -> bool:

Return True if:

Seat is LOCKED

Lock is not expired

locked_by == user_id

Then:

State → BOOKED

Clear locked_by

Return True

Else return False.

⁠

unlock_if_expired(current_time)

UNCHANGED

Still unlocks regardless of user

Clears locked_by

⁠

🆕 force_unlock(user_id)

NEW METHOD — explicitly allowed

def force_unlock(self, user_id: str) -> bool:

Return True if:

Seat is LOCKED

locked_by == user_id

Then:

State → FREE

Clear lock_time

Clear locked_by

Return True

Else return False.

⁠

get_state()

UNCHANGED.

⁠

🧠 Expected Candidate Thinking

Candidate must realize:

Lock ownership is state

Booking is authorization + state

Expiry ignores ownership

Force unlock is controlled unlock

Must NOT break old expiry logic

This tests precision under change.

⁠

🧪 Updated solution.py (Candidate Modifies Existing)

class Seat:

def __init__(self, seat_id: str, lock_duration: int):

pass

def lock(self, current_time: int, user_id: str) -> bool:

pass

def book(self, current_time: int, user_id: str) -> bool:

pass

def unlock_if_expired(self, current_time: int) -> bool:

pass

def force_unlock(self, user_id: str) -> bool:

pass

def get_state(self) -> str:

pass

⚠️ Candidate must update existing implementation, not rewrite.

⁠

🧪 Extension Test File

📄 test_day9_extension.py

from solution import Seat

def test_lock_ownership():

print("Running lock ownership tests...")

seat = Seat("E1", lock_duration=5)

assert seat.lock(10, "user1") is True

assert seat.lock(11, "user2") is False

print("✅ Lock ownership tests passed")

def test_booking_by_owner_only():

print("Running booking ownership tests...")

seat = Seat("E2", lock_duration=5)

seat.lock(10, "user1")

assert seat.book(12, "user2") is False

assert seat.book(12, "user1") is True

assert seat.get_state() == "BOOKED"

print("✅ Booking ownership tests passed")

def test_force_unlock():

print("Running force unlock tests...")

seat = Seat("E3", lock_duration=5)

seat.lock(10, "user1")

assert seat.force_unlock("user2") is False

assert seat.force_unlock("user1") is True

assert seat.get_state() == "FREE"

print("✅ Force unlock tests passed")

def test_expiry_ignores_owner():

print("Running expiry ignores ownership tests...")

seat = Seat("E4", lock_duration=5)

seat.lock(10, "user1")

assert seat.unlock_if_expired(16) is True

assert seat.get_state() == "FREE"

print("✅ Expiry tests passed")

def test_no_actions_after_booked():

print("Running booked state tests...")

seat = Seat("E5", lock_duration=5)

seat.lock(10, "user1")

seat.book(12, "user1")

assert seat.force_unlock("user1") is False

assert seat.unlock_if_expired(20) is False

assert seat.lock(21, "user2") is False

print("✅ Booked state tests passed")

if __name__ == "__main__":

test_lock_ownership()

test_booking_by_owner_only()

test_force_unlock()

test_expiry_ignores_owner()

test_no_actions_after_booked()

print("\n🎉 ALL DAY 9 EXTENSION TESTS PASSED SUCCESSFULLY")

⁠

✅ Pass Criteria for Day 9 Extension

Candidate passes if:

All original Day 9 tests pass

All extension tests pass

Ownership enforced correctly

Expiry logic preserved

Gallery

Want to print your doc?
This is not the way.

Try clicking the ··· in the right corner or using a keyboard shortcut (

CtrlP

) instead.