Zip for combining collections in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of zipping two lists of different lengths?

Consider the following Kotlin code that uses zip to combine two lists of different lengths. What will be printed?

Kotlin

val list1 = listOf("a", "b", "c", "d")
val list2 = listOf(1, 2)
val zipped = list1.zip(list2)
println(zipped)

A [(a, 1), (b, 2), (c, null), (d, null)]

B Compilation error due to different list sizes

C [(a, 1), (b, 2), (c, 3), (d, 4)]

D [(a, 1), (b, 2)]

💡 Hint

Remember that zip pairs elements until the shortest list ends.

The zip function pairs elements from both lists until one list runs out of elements. Since list2 has only 2 elements, the result contains only 2 pairs.

❓ Predict Output

intermediate

What is the output when zipping with a transform function?

What will this Kotlin code print when using zip with a transform lambda?

Kotlin

val nums = listOf(1, 2, 3)
val words = listOf("one", "two", "three")
val result = nums.zip(words) { n, w -> "$w:$n" }
println(result)

A [one:1, two:2, three:3]

B [1:one, 2:two, 3:three]

C [one-1, two-2, three-3]

D Compilation error due to wrong lambda syntax

💡 Hint

The lambda receives elements from the first and second list in order.

The lambda combines each pair as "word:number". So the output is a list of strings like "one:1".

🔧 Debug

advanced

Why does this zip code cause a compilation error?

This Kotlin code tries to zip two lists but causes a compilation error. What is the error?

Kotlin

val a = listOf(1, 2, 3)
val b = listOf("x", "y")
val zipped = a.zip(b) { x -> x.toString() }
println(zipped)

A Lambda must have two parameters, one for each list element

B Lists must be the same size to use zip

C zip requires explicit type arguments for generic parameters

D Cannot zip lists of different types

💡 Hint

Check the lambda parameters for zip with transform.

The zip function with a transform lambda expects two parameters: one from each list. Here, the lambda has only one parameter, causing a compilation error.

❓ Predict Output

advanced

What is the output of zipping a list with itself?

What will this Kotlin code print?

Kotlin

val list = listOf(10, 20, 30)
val zipped = list.zip(list)
println(zipped)

A [(10, 10), (20, 30), (30, 20)]

B [(10, 10), (20, 20), (30, 30)]

C [(10, 20), (20, 30), (30, 10)]

D Compilation error due to zipping list with itself

💡 Hint

Zipping a list with itself pairs elements at the same index.

Zipping pairs elements by index. Since both lists are the same, pairs are identical elements.

🧠 Conceptual

expert

How many pairs are in the zipped list?

Given these Kotlin lists, how many pairs will the zipped list contain?

val first = listOf(1, 2, 3, 4, 5)
val second = listOf("a", "b", "c")

A 8

B 5

C 3

D Compilation error due to different list sizes

💡 Hint

The zipped list length equals the shorter list length.

The zip function stops pairing when the shortest list ends, so the result has 3 pairs.