Project 1 — Design Parking Lot

Problem: Design a parking lot system that manages multiple floors, different spot types, vehicle entry/exit, and fee calculation.

Requirements

Requirement	Details
Multiple floors	Each floor has multiple parking spots
Spot types	Compact, Large, Handicapped, Motorcycle
Park vehicle	Find and assign available spot, generate ticket
Remove vehicle	Calculate fee based on duration and spot type
Availability	Track available spots per floor and type

Class Design

Hover or drag the classes below to inspect fields, methods, and relationship associations.

Design Patterns Used

Pattern	Where	Why
Singleton	ParkingLot	Only one parking lot instance
Strategy	Fee calculation	Different fee strategies (hourly, daily)
Factory	Spot creation	Create spots by type

JavaScript Example

// Enums
const SpotType = { COMPACT: 'COMPACT', LARGE: 'LARGE', HANDICAPPED: 'HANDICAPPED', MOTORCYCLE: 'MOTORCYCLE' };

// ParkingSpot class
class ParkingSpot {
  constructor(id, type) {
    this.id = id;
    this.type = type;
    this.isOccupied = false;
  }
  park() { this.isOccupied = true; }
  removeVehicle() { this.isOccupied = false; }
}

// Ticket class
class Ticket {
  constructor(spot) {
    this.id = Math.random().toString(36).substr(2, 9);
    this.spot = spot;
    this.entryTime = new Date();
    this.exitTime = null;
  }

  calculateFee(strategy) {
    this.exitTime = new Date();
    const hours = (this.exitTime - this.entryTime) / (1000 * 60 * 60);
    return strategy.calculate(hours, this.spot.type);
  }
}

// Fee strategies
class HourlyFeeStrategy {
  calculate(hours, spotType) {
    const rates = { COMPACT: 2, LARGE: 3, HANDICAPPED: 1, MOTORCYCLE: 1.5 };
    return Math.ceil(hours) * (rates[spotType] || 2);
  }
}

// ParkingLot (Singleton)
class ParkingLot {
  static instance = null;

  static getInstance() {
    if (!this.instance) this.instance = new ParkingLot();
    return this.instance;
  }

  constructor() {
    this.floors = [];
  }

  addFloor(floor) { this.floors.push(floor); }

  parkVehicle(spotType) {
    for (const floor of this.floors) {
      const spot = floor.findAvailableSpot(spotType);
      if (spot) {
        spot.park();
        return new Ticket(spot);
      }
    }
    return null;
  }

  removeVehicle(ticket) {
    ticket.spot.removeVehicle();
    return ticket.calculateFee(new HourlyFeeStrategy());
  }
}

Interview Questions

How would you add a reservation system?
How do you handle the case when all spots are full?
How would you implement different pricing for different hours?
How would you add VIP customer priority?