Fold and reduce operations in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the sum of all numbers in the list using fold.

Kotlin

val numbers = listOf(1, 2, 3, 4)
val sum = numbers.fold([1]) { acc, num -> acc + num }
println(sum)

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

A0

B1

Cnull

D""

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as initial value will add 1 extra to the sum.

Using null causes a runtime error.

The fold function starts with an initial value. For summing numbers, the initial value should be 0.

2fill in blank

medium

Complete the code to find the product of all numbers in the list using reduce.

Kotlin

val numbers = listOf(2, 3, 4)
val product = numbers.reduce { acc, num -> acc [1] num }
println(product)

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' will sum instead of multiply.

Using '-' or '/' will give wrong results or errors.

The reduce function combines elements. To get the product, use the multiplication operator '*'.

3fill in blank

hard

Fix the error in the code to correctly concatenate all strings in the list using fold.

Kotlin

val words = listOf("Kotlin", "is", "fun")
val sentence = words.fold([1]) { acc, word -> acc + " " + word }
println(sentence.trim())

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A1

B""

C0

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using null causes a NullPointerException.

Using 0 or 1 causes type mismatch errors.

For string concatenation, the fold initial value should be an empty string "".

4fill in blank

hard

Fill both blanks to create a map of words to their lengths, but only include words longer than 3 characters.

Kotlin

val words = listOf("apple", "bat", "carrot", "dog")
val lengths = words.associateWith { [1] }
val filtered = lengths.filter { it.value [2] 3 }
println(filtered)

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Ait.length

B>

C<

Dit.size

Attempts:

3 left

💡 Hint

Common Mistakes

Using it.size is invalid for String.

Using '<' filters shorter words, not longer.

Use it.length to get the length of each word. Filter words with length greater than 3 using '>'.

5fill in blank

hard

Fill all three blanks to create a map of uppercase words to their lengths, including only words longer than 4 characters.

Kotlin

val words = listOf("tree", "house", "car", "elephant")
val result = words.filter { it.length [1] 4 }
    .associateBy([2]) { [3] }
println(result)

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

A>

Bit.uppercase()

Cit.length

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' filters shorter words.

Using it.lowercase() instead of uppercase.

Swapping key and value in associateBy.

Filter words with length greater than 4 using '>'. Use it.uppercase() as the key and it.length as the value in associateBy.