Enum usage (VehicleType, SpotType) in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Enum Role in Parking Lot Design

In a parking lot system, VehicleType and SpotType enums are used. What is the main purpose of using enums here?

A To restrict vehicle and spot categories to predefined constant values for clarity and safety.

B To allow dynamic creation of vehicle and spot types at runtime.

C To store vehicle and spot data in a database table.

D To randomly assign vehicle types to spots.

💡 Hint

Think about how enums help avoid errors by limiting options.

Enums define fixed sets of constants, ensuring only valid vehicle and spot types are used, improving code safety and readability.

❓ Architecture

intermediate

Mapping VehicleType to SpotType in Design

Which design best represents the relationship between VehicleType and SpotType enums in a parking lot system?

A Each VehicleType maps to one or more compatible SpotTypes to check parking eligibility.

B SpotType values are randomly assigned to VehicleType values without mapping.

C VehicleType and SpotType enums are merged into a single enum for simplicity.

D VehicleType enum contains SpotType values as its members.

💡 Hint

Consider how the system knows which vehicle fits which spot.

Mapping VehicleType to compatible SpotTypes allows the system to validate if a vehicle can park in a given spot type.

❓ scaling

advanced

Scaling Enum Usage for New Vehicle and Spot Types

When adding new vehicle and spot types frequently, what is the best approach to keep the enum usage scalable and maintainable?

A Create a separate enum for each new vehicle and spot type pair.

B Hardcode all new types directly into enums and recompile the system each time.

C Remove enums and use plain strings everywhere for flexibility.

D Use enums with extension mechanisms or configuration files to add new types without code changes.

💡 Hint

Think about how to avoid frequent code changes for new types.

Using extension points or configs allows enums to be flexible while preserving type safety and maintainability.

❓ tradeoff

advanced

Tradeoffs Between Enum and Database Lookup for SpotType

What is a key tradeoff when choosing between using enums or a database table to represent SpotType in a parking system?

A Enums are slower to access than database queries.

B Database tables cannot represent SpotType relationships.

C Enums offer compile-time safety but less flexibility; database allows dynamic updates but adds latency.

D Enums require a database connection to function.

💡 Hint

Consider flexibility versus performance and safety.

Enums provide fixed, fast, and safe values at compile time; databases allow dynamic changes but with overhead and potential errors.

❓ estimation

expert

Estimating Capacity for Enum-Based Parking Spot Allocation

A parking system uses enums for VehicleType and SpotType. Given 3 VehicleTypes and 4 SpotTypes, with each VehicleType compatible with 2 SpotTypes, estimate the minimum number of spot instances needed to support 100 vehicles simultaneously, assuming uniform distribution and no sharing.

A At least 150 spots, assuming some spot types can serve multiple vehicle types.

B Exactly 100 spots, one per vehicle regardless of type.

C At least 200 spots, because each vehicle needs a unique compatible spot.

D At least 300 spots, to cover all combinations of vehicle and spot types.

💡 Hint

Think about how many spots are needed if each vehicle must have a compatible spot without sharing.

To support 100 vehicles simultaneously with no sharing, the minimum number of spot instances required is 100—one per vehicle. Enums ensure compatibility between vehicles and spots but do not increase the total number of spots needed beyond the vehicle count.

Practice

1. What is the main purpose of using enum types like VehicleType and SpotType in system design?

easy

A. To group related constant values and prevent invalid inputs

B. To store large amounts of data efficiently

C. To perform complex mathematical calculations

D. To create user interface elements dynamically

Solution

1. Step 1: Understand enum purpose

   Enums group related constant values, making code clearer and safer.

2. Step 2: Identify benefits in system design

   They prevent invalid values by restricting inputs to predefined options.

3. Final Answer:

   To group related constant values and prevent invalid inputs -> Option A

4. Quick Check:

   Enums = group constants + prevent errors [OK]

Hint: Enums group fixed options to avoid mistakes [OK]

Common Mistakes:

• Thinking enums store large data
• Confusing enums with data structures
• Using enums for UI elements

2. Which of the following is the correct syntax to define an enum VehicleType with values CAR, BIKE, and TRUCK?

easy

A. enum VehicleType = [CAR, BIKE, TRUCK]

B. enum VehicleType { CAR, BIKE, TRUCK }

C. VehicleType = enum(CAR, BIKE, TRUCK)

D. enum VehicleType: CAR, BIKE, TRUCK

Solution

1. Step 1: Recall enum declaration syntax

   Standard enum syntax uses curly braces with comma-separated values.

2. Step 2: Match syntax to options

   enum VehicleType { CAR, BIKE, TRUCK } matches the correct syntax: enum VehicleType { CAR, BIKE, TRUCK }.

3. Final Answer:

   enum VehicleType { CAR, BIKE, TRUCK } -> Option B

4. Quick Check:

   Enum syntax = curly braces + commas [OK]

Hint: Enums use braces and commas for values [OK]

Common Mistakes:

• Using equal sign instead of braces
• Using square brackets for enums
• Missing commas between values

3. Given the enum SpotType { COMPACT, LARGE, HANDICAPPED } and a function that assigns spots based on vehicle type, what will be the output of this code snippet?

VehicleType vehicle = VehicleType.CAR;
SpotType spot;
switch(vehicle) {
  case VehicleType.CAR:
    spot = SpotType.COMPACT;
    break;
  case VehicleType.BIKE:
    spot = SpotType.HANDICAPPED;
    break;
  default:
    spot = SpotType.LARGE;
}
print(spot);

medium

A. Error: VehicleType not handled

B. HANDICAPPED

C. COMPACT

D. LARGE

Solution

1. Step 1: Identify vehicle type value

   VehicleType is set to CAR.

2. Step 2: Follow switch-case logic

   For CAR, spot is assigned COMPACT.

3. Final Answer:

   COMPACT -> Option C

4. Quick Check:

   CAR maps to COMPACT spot [OK]

Hint: Match enum cases carefully in switch [OK]

Common Mistakes:

• Confusing BIKE case with CAR
• Assuming default runs for CAR
• Ignoring break statements

4. Consider this enum usage snippet:

enum VehicleType { CAR, BIKE, TRUCK }

void assignSpot(VehicleType v) {
  if (v == VehicleType.CAR) {
    print("Compact Spot");
  } else if (v == VehicleType.BIKE) {
    print("Bike Spot");
  }
}

What is the problem if assignSpot(VehicleType.TRUCK) is called?

medium

A. Prints "Bike Spot" incorrectly

B. Syntax error due to missing TRUCK case

C. Runtime error because TRUCK is invalid

D. No output because TRUCK case is not handled

Solution

1. Step 1: Analyze if-else conditions

   Only CAR and BIKE cases are handled explicitly.

2. Step 2: Consider TRUCK input

   TRUCK does not match any condition, so no print occurs.

3. Final Answer:

   No output because TRUCK case is not handled -> Option D

4. Quick Check:

   Unhandled enum value = no output [OK]

Hint: Always handle all enum values or add default [OK]

Common Mistakes:

• Expecting syntax or runtime error
• Assuming default print happens
• Confusing enum invalidity

5. In a parking system, you have enums VehicleType { CAR, BIKE, TRUCK } and SpotType { COMPACT, LARGE, HANDICAPPED }. You want to assign spots such that:
- Cars use COMPACT spots
- Bikes use HANDICAPPED spots
- Trucks use LARGE spots

Which design approach best ensures no invalid spot assignment happens?

hard

A. Use a mapping dictionary from VehicleType to SpotType and validate assignments

B. Use separate if-else blocks without enums for flexibility

C. Assign spots randomly and check later if valid

D. Use strings instead of enums for vehicle and spot types

Solution

1. Step 1: Understand enum benefits for mapping

   Enums provide fixed sets, so mapping ensures clear, valid assignments.

2. Step 2: Evaluate design options

   Mapping dictionary with enums enforces rules and prevents invalid spots.

3. Final Answer:

   Use a mapping dictionary from VehicleType to SpotType and validate assignments -> Option A

4. Quick Check:

   Mapping enums = safe, clear assignments [OK]

Hint: Map enums directly to enforce valid pairs [OK]

Common Mistakes:

• Using strings loses type safety
• Random assignment causes errors
• If-else without enums is error-prone