State management (idle, moving up, moving down) in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding state transitions in a simple elevator system

Consider a system managing an elevator with three states: idle, moving up, and moving down. Which of the following best describes the correct state transition when the elevator receives a request to move to a higher floor?

A From moving up to idle, then moving down immediately.

B From moving down directly to moving up without going idle.

C From idle to moving down, then to moving up after reaching the floor.

D From idle to moving up, then to idle after reaching the floor.

💡 Hint

Think about the natural flow of elevator movement when going to a higher floor.

The elevator starts idle, then moves up when requested to a higher floor, and returns to idle once it reaches the destination.

❓ Architecture

intermediate

Designing a state machine for elevator movement

You need to design a state machine for an elevator with states: idle, moving up, moving down. Which component is essential to handle state transitions correctly?

A A controller that listens to floor requests and updates the state accordingly.

B A database to store all floor requests permanently.

C A UI component to display elevator status only.

D A logging system to record elevator movements.

💡 Hint

Focus on what controls the state changes in the system.

The controller is responsible for receiving requests and changing the elevator's state based on those requests.

❓ scaling

advanced

Scaling state management for multiple elevators

When managing multiple elevators in a building, what is the best approach to maintain consistent state management across all elevators?

A Let each elevator manage its own state independently without coordination.

B Use a centralized state manager that tracks all elevators and their states.

C Store elevator states only in local memory without synchronization.

D Use a random assignment of states to elevators to balance load.

💡 Hint

Consider how to avoid conflicting states and optimize elevator usage.

A centralized state manager ensures all elevators' states are tracked and coordinated to optimize performance and avoid conflicts.

❓ tradeoff

advanced

Tradeoffs in state polling vs event-driven updates

For an elevator system managing states (idle, moving up, moving down), which tradeoff is true when choosing between polling the elevator state frequently versus using event-driven updates?

A Polling and event-driven approaches have identical system load and complexity.

B Polling reduces system load and complexity; event-driven increases load and complexity.

C Polling increases system load but simplifies state detection; event-driven reduces load but requires more complex event handling.

D Event-driven updates always cause delays compared to polling.

💡 Hint

Think about how often the system checks for changes and how it reacts.

Polling checks state regularly, increasing load but is simple; event-driven updates only on changes, reducing load but needing event management.

❓ estimation

expert

Estimating capacity for state management in a high-rise elevator system

You are designing state management for 20 elevators in a 100-floor building. Each elevator changes state approximately every 10 seconds on average. Estimate the number of state transitions the system must handle per minute.

A 120 transitions per minute

B 60 transitions per minute

C 200 transitions per minute

D 100 transitions per minute

💡 Hint

Calculate transitions per elevator per minute, then multiply by number of elevators.

Each elevator changes state every 10 seconds → 6 times per minute (60/10=6). For 20 elevators: 6 × 20 = 120 transitions per minute.