Set creation (setOf, mutableSetOf) in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an immutable set with elements 1, 2, and 3.

Kotlin

val numbers = [1](1, 2, 3)

Drag options to blanks, or click blank then click option'

AmutableSetOf

BlistOf

CsetOf

DarrayOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableSetOf creates a mutable set, not immutable.

Using listOf creates a list, not a set.

Use setOf to create an immutable set in Kotlin.

2fill in blank

medium

Complete the code to create a mutable set with elements "apple" and "banana".

Kotlin

val fruits = [1]("apple", "banana")

Drag options to blanks, or click blank then click option'

AsetOf

BmutableSetOf

CarrayOf

DlistOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using setOf creates an immutable set that cannot be changed.

Using listOf creates a list, not a set.

Use mutableSetOf to create a set that you can change later.

3fill in blank

hard

Fix the error in the code to create an immutable set of integers.

Kotlin

val nums = setOf[1]1, 2, 3)

Drag options to blanks, or click blank then click option'

A(

B[

C{

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets or curly braces instead of parentheses.

Missing the opening parenthesis.

The setOf function requires parentheses around its arguments.

4fill in blank

hard

Fill both blanks to create a mutable set and add an element "orange".

Kotlin

val fruits = [1]("apple", "banana")
fruits.[2]("orange")

Drag options to blanks, or click blank then click option'

AmutableSetOf

BsetOf

Cadd

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using setOf creates an immutable set that cannot add elements.

Using remove instead of add to insert elements.

Use mutableSetOf to create a mutable set and add to insert a new element.

5fill in blank

hard

Fill all three blanks to create an immutable set of numbers, check if it contains 5, and print the result.

Kotlin

val numbers = [1](1, 2, 3, 4, 5)
val hasFive = numbers.[2](5)
println([3])

Drag options to blanks, or click blank then click option'

AsetOf

Bcontains

ChasFive

DmutableSetOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using mutableSetOf instead of setOf for immutable set.

Printing the function call instead of the variable.

Using wrong method to check membership.

Create an immutable set with setOf, check membership with contains, and print the boolean variable.

Practice

1. What does the Kotlin function setOf(1, 2, 2, 3) return?

easy

A. A list containing elements: 1, 2, 2, 3

B. A set containing duplicates: 1, 2, 2, 3

C. A set containing unique elements: 1, 2, 3

D. An error because of duplicate elements

Solution

1. Step 1: Understand setOf behavior

   setOf creates a set that holds only unique elements, automatically removing duplicates.

2. Step 2: Analyze the input elements

   The input has elements 1, 2, 2, 3. The duplicate 2 is ignored in the set.

3. Final Answer:

   A set containing unique elements: 1, 2, 3 -> Option C

4. Quick Check:

   setOf removes duplicates = unique elements [OK]

Hint: Remember: sets keep only unique items [OK]

Common Mistakes:

• Thinking sets keep duplicates like lists
• Confusing setOf with listOf
• Expecting an error for duplicates

2. Which of the following is the correct way to create a mutable set of strings in Kotlin?

easy

A. val mySet = mutableSetOf<String>("apple", "banana")

B. val mySet = setOf<String>("apple", "banana")

C. val mySet = mutableSet("apple", "banana")

D. val mySet = mutableSetOf("apple", "banana")

Solution

1. Step 1: Identify correct syntax for mutableSetOf

   The correct function is mutableSetOf with type parameter and parentheses.

2. Step 2: Check each option

   val mySet = mutableSetOf<String>("apple", "banana") uses mutableSetOf<String>("apple", "banana"), which is correct. val mySet = setOf<String>("apple", "banana") uses setOf which creates an immutable set. val mySet = mutableSet("apple", "banana") uses a non-existent function mutableSet. val mySet = mutableSetOf("apple", "banana") has a syntax error with an extra quote.

3. Final Answer:

   val mySet = mutableSetOf<String>("apple", "banana") -> Option A

4. Quick Check:

   mutableSetOf syntax correct = val mySet = mutableSetOf<String>("apple", "banana") [OK]

Hint: Use mutableSetOf() to create changeable sets [OK]

Common Mistakes:

• Using setOf instead of mutableSetOf for mutable sets
• Misspelling mutableSetOf
• Syntax errors with quotes or parentheses

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

val numbers = mutableSetOf(1, 2, 3)
numbers.add(2)
numbers.add(4)
println(numbers)

medium

A. Compilation error

B. [1, 2, 3, 2, 4]

C. [1, 2, 3]

D. [1, 2, 3, 4]

Solution

1. Step 1: Understand mutableSetOf and add behavior

   The set starts with 1, 2, 3. Adding 2 again does nothing because sets ignore duplicates. Adding 4 adds a new element.

2. Step 2: Determine final set contents

   After additions, the set contains 1, 2, 3, and 4.

3. Final Answer:

   [1, 2, 3, 4] -> Option D

4. Quick Check:

   Sets ignore duplicates, so 2 is not added twice [OK]

Hint: Adding duplicates to sets does nothing [OK]

Common Mistakes:

• Expecting duplicates to appear in output
• Confusing set print format with list
• Thinking add returns error on duplicates

4. Identify the error in this Kotlin code snippet:

val fruits = setOf("apple", "banana")
fruits.add("orange")
println(fruits)

medium

A. Syntax error in setOf declaration

B. Cannot add elements to an immutable set

C. Missing import for setOf

D. No error, code runs fine

Solution

1. Step 1: Check mutability of setOf

   setOf creates an immutable set that cannot be changed after creation.

2. Step 2: Analyze the add operation

   Calling add on an immutable set causes a compilation error because the set cannot be modified.

3. Final Answer:

   Cannot add elements to an immutable set -> Option B

4. Quick Check:

   setOf = immutable, add() not allowed [OK]

Hint: Use mutableSetOf to add or remove items [OK]

Common Mistakes:

• Trying to modify immutable sets
• Confusing setOf with mutableSetOf
• Ignoring compiler error messages

5. You want to create a mutable set of integers from a list but only include numbers greater than 5. Which Kotlin code correctly does this?

hard

A. val nums = mutableSetOf(1, 6, 8, 3, 7).filterTo(mutableSetOf()) { it > 5 }

B. val nums = setOf(1, 6, 8, 3, 7).filter { it > 5 }.toSet()

C. val nums = mutableSetOf(1, 6, 8, 3, 7).filter { it > 5 }

D. val nums = mutableSetOf(1, 6, 8, 3, 7).filter { it > 5 }.toSet()

Solution

1. Step 1: Understand filtering and set creation

   We want a mutable set with only numbers > 5. Using filterTo with a mutable set collects filtered items directly into a mutable set.

2. Step 2: Evaluate each option

   val nums = mutableSetOf(1, 6, 8, 3, 7).filter { it > 5 } returns a List, not a mutable set. val nums = mutableSetOf(1, 6, 8, 3, 7).filterTo(mutableSetOf()) { it > 5 } correctly filters into a mutable set. val nums = setOf(1, 6, 8, 3, 7).filter { it > 5 }.toSet() creates an immutable set first, then filters to list and toSet(), producing an immutable set, not mutable. val nums = mutableSetOf(1, 6, 8, 3, 7).filter { it > 5 }.toSet() filters to a list then toSet(), producing an immutable set, not mutable.

3. Final Answer:

   val nums = mutableSetOf(1, 6, 8, 3, 7).filterTo(mutableSetOf()) { it > 5 } -> Option A

4. Quick Check:

   filterTo with mutableSetOf creates mutable set directly [OK]

Hint: Use filterTo(mutableSetOf()) for filtered mutable sets [OK]

Common Mistakes:

• Using filter() returns list, not set
• Not converting to mutable set after filtering
• Confusing setOf and mutableSetOf usage