Collection size and emptiness checks in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Check if a list is empty using Kotlin

Given the Kotlin list val fruits = listOf("apple", "banana", "cherry"), what is the output of fruits.isEmpty()?

Kotlin

val fruits = listOf("apple", "banana", "cherry")
println(fruits.isEmpty())

A false

B true

C null

D Compilation error

💡 Hint

Think about whether the list has any items inside.

The isEmpty() function returns true if the list has no elements. Since fruits has three items, it returns false.

❓ query_result

intermediate

Count elements in a Kotlin set

What is the output of the following Kotlin code?

val numbers = setOf(1, 2, 3, 4, 5)
println(numbers.size)

Kotlin

val numbers = setOf(1, 2, 3, 4, 5)
println(numbers.size)

A 0

B 4

C Compilation error

D 5

💡 Hint

Count how many unique numbers are in the set.

The size property returns the number of elements in the set. Here, there are 5 unique numbers, so the output is 5.

📝 Syntax

advanced

Identify the correct way to check if a Kotlin map is empty

Which of the following Kotlin expressions correctly checks if the map val map = mapOf("a" to 1, "b" to 2) is empty?

Kotlin

val map = mapOf("a" to 1, "b" to 2)

A map.isEmpty()

B map.empty()

C map.size == null

D map.isEmpty

💡 Hint

Look for the standard Kotlin function to check emptiness.

The correct function to check if a collection is empty in Kotlin is isEmpty(). The other options are either invalid or incorrect syntax.

❓ query_result

advanced

Result of filtering a list and checking size

What is the output of this Kotlin code?

val nums = listOf(1, 2, 3, 4, 5)
val filtered = nums.filter { it > 3 }
println(filtered.size)

Kotlin

val nums = listOf(1, 2, 3, 4, 5)
val filtered = nums.filter { it > 3 }
println(filtered.size)

A 3

B 2

C 5

D 0

💡 Hint

Count how many numbers are greater than 3.

The filter keeps numbers greater than 3: 4 and 5. So the filtered list has 2 elements, and filtered.size is 2.

🧠 Conceptual

expert

Understanding Kotlin collection emptiness and size properties

Consider a Kotlin collection val col = listOf(). Which statement is true about col.isEmpty() and col.size?

A <code>col.isEmpty()</code> returns false and <code>col.size</code> returns 0

B <code>col.isEmpty()</code> returns true and <code>col.size</code> returns null

C <code>col.isEmpty()</code> returns true and <code>col.size</code> returns 0

D <code>col.isEmpty()</code> returns false and <code>col.size</code> returns null

💡 Hint

Think about what an empty list means for size and emptiness.

An empty list has no elements, so isEmpty() returns true. The size property returns the number of elements, which is 0 for an empty list.