Multiple elevator coordination in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Elevator request assignment strategy

In a building with multiple elevators, which strategy best minimizes average wait time for passengers?

A Assign the request to the elevator that is currently idle on the ground floor.

B Assign the request to the elevator with the fewest passengers regardless of location.

C Assign the request randomly to any elevator to balance load.

D Assign the request to the elevator closest to the pickup floor and moving towards it.

💡 Hint

Think about which elevator can reach the passenger fastest without unnecessary detours.

Assigning the request to the closest elevator moving towards the pickup floor reduces wait time by avoiding unnecessary travel.

❓ Architecture

intermediate

Component responsible for elevator state tracking

Which component in a multiple elevator system is primarily responsible for tracking each elevator's current floor, direction, and door status?

A Elevator Controller Module

B Elevator State Manager

C User Interface Module

D Request Dispatcher Module

💡 Hint

Consider which module holds real-time data about elevator positions and statuses.

The Elevator State Manager maintains real-time information about each elevator's floor, direction, and door status to enable coordination.

❓ scaling

advanced

Scaling elevator coordination for a skyscraper

When scaling a multiple elevator system for a 100-floor skyscraper with 20 elevators, which approach best maintains system responsiveness?

A Divide elevators into groups serving specific floor ranges and coordinate requests within groups.

B Use a single centralized controller to manage all elevators and requests.

C Assign requests randomly to any elevator regardless of floor range.

D Let each elevator operate independently without coordination.

💡 Hint

Think about reducing communication overhead and improving response time by limiting coordination scope.

Grouping elevators by floor ranges reduces complexity and improves responsiveness by localizing coordination.

❓ tradeoff

advanced

Tradeoff between energy efficiency and wait time

In multiple elevator coordination, prioritizing energy efficiency by minimizing elevator movement can increase passenger wait times. Which design choice best balances this tradeoff?

A Always keep elevators idle at the ground floor to save energy.

B Serve requests strictly in the order they arrive without optimization.

C Implement a dynamic scheduling algorithm that adapts based on current traffic patterns.

D Use fixed elevator routes regardless of demand.

💡 Hint

Consider a system that changes behavior based on real-time usage to optimize both goals.

Dynamic scheduling adapts to traffic, balancing energy use and wait times effectively.

❓ estimation

expert

Estimating peak load capacity for multiple elevators

Given a building with 15 elevators and 50 floors, estimate the maximum number of passengers the system can transport per hour during peak times assuming each elevator holds 20 passengers and completes 4 full trips per hour.

A 1200 passengers per hour

B 1500 passengers per hour

C 1000 passengers per hour

D 3000 passengers per hour

💡 Hint

Calculate total capacity by multiplying elevators, capacity per elevator, and trips per hour.

15 elevators × 20 passengers × 4 trips = 1200 passengers per hour.