Associate for map creation in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code using associate?

Consider the following Kotlin code snippet that creates a map from a list of strings using associate. What will be printed?

Kotlin

val fruits = listOf("apple", "banana", "cherry")
val map = fruits.associate { it to it.length }
println(map)

A Compilation error

B {apple=5, banana=6, cherry=7}

C {apple=4, banana=6, cherry=6}

D {apple=5, banana=6, cherry=6}

💡 Hint

Remember that associate creates a map where each key-value pair is defined by the lambda.

The associate function creates a map where each string is the key and its length is the value. The lengths are correct as apple=5, banana=6, cherry=6.

❓ Predict Output

intermediate

What does this Kotlin code print when using associateBy?

Look at this Kotlin code that uses associateBy. What is the output?

Kotlin

data class Person(val name: String, val age: Int)

val people = listOf(Person("Alice", 30), Person("Bob", 25), Person("Charlie", 30))
val map = people.associateBy { it.age }
println(map)

A {30=Person(name=Alice, age=30), 25=Person(name=Charlie, age=30)}

B {30=Person(name=Alice, age=30), 25=Person(name=Bob, age=25)}

C {30=Person(name=Charlie, age=30), 25=Person(name=Bob, age=25)}

D Runtime exception

💡 Hint

When keys are duplicated, the last element wins in associateBy.

associateBy creates a map where the key is the age. Since two people have age 30, the last one (Charlie) overwrites Alice.

🔧 Debug

advanced

Why does this Kotlin code cause a compilation error?

Examine this Kotlin code snippet. It tries to create a map using associate but fails to compile. What is the cause?

Kotlin

val numbers = listOf(1, 2, 3)
val map = numbers.associate { it * 2 }
println(map)

A The list cannot be used with associate on Int elements.

B The println statement is missing parentheses.

C The associate function requires a map as input.

D The lambda must return a Pair, but it returns an Int.

💡 Hint

Check what the lambda inside associate should return.

The associate function expects the lambda to return a Pair<K, V> for each element. Returning just an Int causes a compilation error.

❓ Predict Output

advanced

What is the output of this Kotlin code using associateWith?

Given this Kotlin code using associateWith, what will be printed?

Kotlin

val words = listOf("one", "two", "three")
val map = words.associateWith { it.length }
println(map)

A {one=3, two=3, three=5}

B {3=one, 3=two, 5=three}

C {one=3, two=3, three=6}

D Compilation error

💡 Hint

associateWith creates a map where each element is the key and the lambda result is the value.

The map keys are the words themselves, and the values are their lengths: one=3, two=3, three=5.

🧠 Conceptual

expert

How many entries are in the map created by this Kotlin code?

Consider this Kotlin code that creates a map from a list of pairs using associate. How many entries will the resulting map have?

Kotlin

val pairs = listOf("a" to 1, "b" to 2, "a" to 3, "c" to 4)
val map = pairs.associate { it }
println(map.size)

A 3

B 4

C 2

D Compilation error

💡 Hint

When keys repeat, the last value overwrites previous ones in a map.

The key "a" appears twice. The last value (3) overwrites the first (1). So keys are "a", "b", "c" → 3 entries.