Enum class declaration in Kotlin - Time & Space Complexity

Time Complexity: Enum class declaration

O(n)

Understanding Time Complexity

Let's see how the time it takes to run code changes when we use an enum class in Kotlin.

We want to know how the program's work grows as we use more enum values.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

enum class Direction {
    NORTH, SOUTH, EAST, WEST
}

fun printDirections() {
    for (dir in Direction.values()) {
        println(dir)
    }
}

This code defines an enum with four directions and prints each one.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through all enum values using Direction.values().
• How many times: Once for each enum constant (4 times here).

How Execution Grows With Input

As the number of enum values grows, the loop runs once for each value.

Input Size (n)	Approx. Operations
4	4 (one print per direction)
10	10
100	100

Pattern observation: The work grows directly with the number of enum values.

Final Time Complexity

Time Complexity: O(n)

This means the time to run grows in a straight line with the number of enum entries.

Common Mistake

[X] Wrong: "Enum classes run in constant time no matter how many values they have."

[OK] Correct: Because looping through all enum values takes time proportional to how many values exist.

Interview Connect

Understanding how enum classes work helps you explain simple loops and collections clearly, a skill useful in many coding discussions.

Self-Check

"What if we replaced the loop with a function that looks up a single enum value by name? How would the time complexity change?"

Practice

1. What is the main purpose of an enum class in Kotlin?

easy

A. To define a function that returns multiple values

B. To group a fixed set of related constants under one type

C. To create a class that can be instantiated multiple times

D. To declare a variable that can hold any data type

Solution

1. Step 1: Understand enum class purpose

   An enum class is designed to hold a fixed set of constants that belong together logically.

2. Step 2: Compare options with enum usage

   Only To group a fixed set of related constants under one type correctly describes grouping related constants under one type, which is the main use of enum classes.

3. Final Answer:

   To group a fixed set of related constants under one type -> Option B

4. Quick Check:

   Enum class purpose = group constants [OK]

Hint: Enums group fixed constants for clarity and safety [OK]

Common Mistakes:

• Thinking enums are for creating multiple instances
• Confusing enums with regular classes
• Believing enums can hold any data type variable

2. Which of the following is the correct syntax to declare an enum class named Direction with constants NORTH, SOUTH, EAST, and WEST?

easy

A. enum class Direction { NORTH, SOUTH, EAST, WEST }

B. class enum Direction { NORTH, SOUTH, EAST, WEST }

C. enum Direction { NORTH; SOUTH; EAST; WEST }

D. enum class Direction = (NORTH, SOUTH, EAST, WEST)

Solution

1. Step 1: Recall Kotlin enum class syntax

   Kotlin enum classes start with enum class followed by the name and curly braces containing constants separated by commas.

2. Step 2: Check each option's syntax

   enum class Direction { NORTH, SOUTH, EAST, WEST } matches the correct syntax. Options A, C, and D have incorrect keywords, punctuation, or structure.

3. Final Answer:

   enum class Direction { NORTH, SOUTH, EAST, WEST } -> Option A

4. Quick Check:

   Correct enum syntax = enum class Direction { NORTH, SOUTH, EAST, WEST } [OK]

Hint: Use 'enum class Name { CONST1, CONST2 }' syntax [OK]

Common Mistakes:

• Using 'class enum' instead of 'enum class'
• Separating constants with semicolons instead of commas
• Assigning enum constants with '=' instead of listing

3. What will be the output of the following Kotlin code?

enum class Color { RED, GREEN, BLUE }
fun main() {
    val c = Color.GREEN
    println(c.name)
}

medium

A. green

B. Color.GREEN

C. 1

D. GREEN

Solution

1. Step 1: Understand enum constant property 'name'

   Each enum constant has a built-in name property that returns its exact name as a string.

2. Step 2: Analyze the code output

   The code prints c.name where c is Color.GREEN, so it prints "GREEN" exactly as declared.

3. Final Answer:

   GREEN -> Option D

4. Quick Check:

   Enum constant name property = GREEN [OK]

Hint: Enum.name returns constant name as string [OK]

Common Mistakes:

• Expecting lowercase output
• Printing enum constant directly without .name
• Confusing ordinal number with name

4. Identify the error in this Kotlin enum class declaration:

enum class Size {
    SMALL,
    MEDIUM
    LARGE
}

medium

A. Cannot declare enum class without constructor

B. Enum constants must be lowercase

C. Missing comma after MEDIUM

D. Enum class must have at least 5 constants

Solution

1. Step 1: Check enum constants separation

   Enum constants must be separated by commas except the last one. Here, MEDIUM is missing a comma after it.

2. Step 2: Validate other options

   Constants can be uppercase, no constructor is required, and no minimum count is needed. So only missing comma is the error.

3. Final Answer:

   Missing comma after MEDIUM -> Option C

4. Quick Check:

   Enum constants separated by commas [OK]

Hint: Separate enum constants with commas except last [OK]

Common Mistakes:

• Omitting commas between constants
• Using lowercase for constants (not required)
• Thinking constructor is mandatory

5. How can you add a property rgb to an enum class Color that stores the color's RGB integer value, and access it for Color.RED? Choose the correct code snippet.

hard

A. enum class Color(val rgb: Int) { RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF) }
fun main() { println(Color.RED.rgb) }

B. enum class Color { RED = 0xFF0000, GREEN = 0x00FF00, BLUE = 0x0000FF }
fun main() { println(Color.RED.rgb) }

C. enum class Color { RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF) }
fun main() { println(Color.RED.rgb) }

D. enum class Color { RED, GREEN, BLUE }
fun main() { println(Color.RED.rgb) }

Solution

1. Step 1: Understand enum property declaration

   To add a property, declare a constructor parameter in the enum class and pass values to each constant.

2. Step 2: Check each option for correct syntax

   enum class Color(val rgb: Int) { RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF) } fun main() { println(Color.RED.rgb) } correctly declares val rgb: Int in constructor and assigns values. enum class Color { RED = 0xFF0000, GREEN = 0x00FF00, BLUE = 0x0000FF } fun main() { println(Color.RED.rgb) } uses invalid assignment syntax. enum class Color { RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF) } fun main() { println(Color.RED.rgb) } misses constructor declaration. enum class Color { RED, GREEN, BLUE } fun main() { println(Color.RED.rgb) } has no property defined.

3. Final Answer:

   enum class Color(val rgb: Int) { RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF) } fun main() { println(Color.RED.rgb) } -> Option A

4. Quick Check:

   Enum property via constructor = enum class Color(val rgb: Int) { RED(0xFF0000), GREEN(0x00FF00), BLUE(0x0000FF) } fun main() { println(Color.RED.rgb) } [OK]

Hint: Add properties via constructor parameters in enum class [OK]

Common Mistakes:

• Trying to assign values with '=' inside enum constants
• Not declaring constructor parameters in enum class
• Accessing property that was never declared